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Full text of "Crop rotation, tillage, and fertility experiments at the Lawton (Okla.) Field Station, 1917-49"

Historic, archived document 

Do not assume content reflects current 
scientific knowledge, policies, or practices 



UNITED STATES 

DEPARTMENT OF AGRICULTURE 

LIBRARY 




Book number 



922077 



1 

Ag84C 

951-975 

1954-1955 



?H1 
■3 



CROP ROTATION, 
TILLAGE, AND 
FERTILITY 
EXPERIMENTS 

CURRENT SFoa,, *f* ^ 



* MAR 9,955 



at the 

LAWTON (OKLA.) 

FIELD STATION, 1917-49 



Circular No. 951 
UNITED STATES DEPARTMENT OF AGRICULTURE 



CROP ROTATION. 
TILLAGE, AND 
FERTILITY 
EXPERIMENTS 
at^ the 

LAWTON (OKLA.) 
FIELD STATION, 
1917-49 



By W. M. OSBORN, formerly associate agronomist, and 
O. R. MATHEWS, senior agronomist, Soil and Water Con- 
servation Research Branch, Agricultural Research Service 



UNITED STATES DEPARTMENT OF AGRICULTURE 

In cooperation with the Oklahoma Agricultural Experiment Station 
Circular 951 January 1955 



CONTENTS 



Page 

Introduction 1 

Climate 3 

Precipitation 3 

Temperatures and frost-free 

period 4 

Wind velocity 4 

Evaporation 4 

Soil characteristics 5 

Crop hazards other than those of 

climate 7 

Plant diseases 7 

Destructive insects. 9 

Bird damage 9 

Soil erosion 10 

Procedure in rotation and tillage 

experiments 11 

Yields and relative adaptation of 

crops 14 

Tillage and sequence results 18 

Winter wheat 18 

Cotton 22 

Sorghums 24 

Cowpeas 27 

Corn 27 

ii 



Tillage and sequence results — Con. 

Oats and barley 

Alfalfa and sweetclbver 

Date-of-seeding and variety tests 
of winter barley 

Comparison of fall-sown and 
spring-sown oats 

Nitrogen content of cropped soil. 

Tests with commercial fertilizers. 
Seed yields of weeping love- 
grass 

Sorghum 

Wheat and oats 

Cotton 

Results with grapes, trees, 

shrubs, and grasses 

Grapes 

Trees and ornamental shrubs _ 
Grasses 

Cropping systems adapted to 
the area 

Summary and conclusion 

Literature cited 

Append ix 



For sale by the Superintendent of Documents, U. S. Government Printing Office 
Washington 25, D. C. - Price 25 cents 



922077 



Crop Rotation, Tillage, and Fertility Experiments at 
the Lawton (Okla.) Field Station, 1917-49 

By W. M. Osborn, formerly associate agronomist, and O. R. Mathews, senior 
agronomist, Soil and Water Conservation Research Branch, Agricultural Research 
Service 

INTRODUCTION 

Southwestern Oklahoma 1 lies close to the eastern limit of the 
southern Great Plains. It is drained by intermittent streams, tribu- 
tary to the Red River, which flow south by east. Most of the streams 
are small but frequently overflow with considerable damage to adjacent 
bottom lands. Much of the farmland bordering creeks and rivers is 
highly productive for alfalfa, cotton, and broomcorn. 

This area was opened to homesteading in 1901. Since then it has 
undergone a rapid transition from well-grassed plains supporting large 
herds of grazing beef cattle to cropped lands with numerous farm 
homes. The settler who came to southwest Oklahoma in 1901 could 
not plan his .farming in the light of any local experience. Typically, 
after breaking the native sod he planted crops that were grown in some 
area where he had previously farmed, and tilled them by methods to 
which he had been accustomed. The settlers came chiefly from less 
arid areas in States such as Iowa, Kansas, Missouri, Arkansas, and 
Texas. Harassed by devastating storms, heat, frost, floods, and 
drought, most of them soon tried to change to crops and tillage 
methods better adapted to the local climate. This effort involved 
many mistakes. More than 15 years passed before any agricultural 
research agency directly serving the area had begun to supply infor- 
mation helpful to the farmer. In the meantime, however, some 
keenly observant settlers had avoided most of the common mistakes 
and developed cropping practices that were well adapted to local 
conditions. 

The native grass range at the time of white settlement was composed 
chiefly of big bluestem {Andropogon gerardi), little bluestem (A. 
scoparius), side-oats grama (Bouteloua curtipendula) , blue grama (B. 
gracilis), and buffalo grass (Buchloe dactyloides) . As the farms de- 
veloped, acreages available for grazing became restricted and over- 
grazing resulted. Less desirable native grasses, some with a short 
season and all with lower palatability, became established in the 
native pastures and reduced their value. The more important of 
these were switchgrass {Panicum, mrgatum), downy chess (Bromus 
tectorum, commonly known as cheat grass) , and dropseed (Sporobolus 
sp-)- 

1 The area referred to in this publication as southwestern Oklahoma includes 
roughly these counties: Grady, Stephens, Jefferson, Caddo, Comanche, Cotton, 
Custer, Washita, Kiowa, Tillman, Beckham, Greer, Jackson, and Harmon. 
Research findings presented here apply not only to this area but to a contiguous 
part of northern Texas. 



2 CIRCULAR 951, U. S. DEPARTMENT OF AGRICULTURE 

During the transition from vast unfenced grazing areas to farms 
and ranches, a heavy toll was taken by droughts, floods, destructive 
crop insects, and erosion. Use of better adapted crops and improved 
farm practices have reduced crop hazards. Reseeding of wornout or 
overgrazed farmlands with native and introduced grasses has met 
with moderate to good success. 

The long growing season of southwestern Oklahoma permits pro- 
duction of a wide variety of crops, of which the more important are 
cotton, alfalfa and other legumes, grain and forage sorghums, and — 
except on the sandy soils — wheat, barley, and oats. These more 
important crops are grown in rotations. The small grains have now 
become much more valuable because they are used not only as cash 
crops but for grazing and because improved varieties and production 
methods have been developed. Alfalfa acreage on creek and river 
bottom land in the area has gradually increased, and the crop is highly 
important on these restricted areas. Early maturing corn has been 
and is being grown with moderate success on bottom lands and on 
sandy soils. The value of sweetclover as a soil-building crop has led 
to many efforts to include it in cropping systems in the area, and 
these efforts have been moderately successful in years of well-distrib- 
uted rainfall. Hairy vetch is now finding an important place in 
cropping systems for the sandy soils of southwestern Oklahoma. 

The Lawton Field Station was established by the Federal Govern- 
ment at Lawton, in Comanche County, Okla., in 1915 to study the 
crop possibilities and limitations of southwestern Oklahoma. The 
station's experimental area was then in virgin sod. Its first crop was 
grown in 1916 on land broken from sod in 1915 and uniformly pre- 
pared. From 1917 on, the major field crops of the area were grown 
at the station in fixed sequences, by various tillage methods. Co- 
operation was maintained formally or informally with the Oklahoma 
Agricultural Experiment Station; the Divisions of Cotton and Other 
Fiber Crops and Diseases, Cereal Crops and Diseases, and Cereal and 
Forage Insects of the United States Department of Agriculture; the 
United States Weather Bureau; and the Kiowa Indian Agency. In 
1949 the station was discontinued and the land turned back to the 
Kiowa Indian School. This publication principally summarizes the 
experimental work in crop rotation and tillage from 1924 through 
1949. It briefly discusses work of the station along other lines that 
has not been reported elsewhere — date-of-seeding and variety tests 
of winter barley, a comparison of fall-sown and spring-sown oats, a 
study of the nitrogen content of the soil as affected by cropping, and 
experiments in using commercial fertilizers, in seeding grasses, and in 
growing grapes, trees, and ornamental shrubs. Together with 
experimental results it presents some observations on general experi- 
ence and present-day trends in practical agriculture in southwestern 
Oklahoma. 

Work done at the station has previously been reported in journal 
articles, in 8 bulletins of the Oklahoma Agricultural Experiment 
Station, and in 1 bulletin of the Department of Agriculture (5, 10, 
IS, 18,20,22,24-28)? 



2 Italic numbers in parentheses refer to Literature Cited, p. 44. 



CHOP ROTATION, TILLAGE, AND FERTILITY EXPERIMENTS 3 

CLIMATE 

PRECIPITATION 

Annual precipitation at the Lawton station in the period 1916-49 
averaged 28.70 inches. It ranged from 17.23 inches in 1939 to 43.92 
inches in 1941 . Among monthly precipitation averages of the growing 
season those for July and August were the lowest. Monthly pre- 
cipitation reached its spring and fall peaks in May and October (fig. 1). 



ANNUAL , 28.70 




JAN. FEB. MAR. APR. MAY JUNE JULY AUG. SEPTOCT. NOV. DEC. 



Figure 1.- — Monthly averages of precipitation at the Lawton Field Station, 

1916-49. 



On an average, 63 percent of the annual precipitation occurred during 
the 6-month period April-September. The extremes in precipitation 
totals for each month of the growing season were as follows: 

Precipitation extremes in 1916-49 

Minimum Maximum 

Month Inches Inches 

April 0. 01 6. 85 

May .90 14.12 

June .25 8.01 

July .07 6.28 

August 7.48 

September 10.36 

October . 03 13. 78 



4 CIRCULAR 951, U. S. DEPARTMENT OF AGRICULTURE 

Southwestern Oklahoma's average yearly total of precipitation is 
sufficient to make the area subhumid rather than semiarid if the 
yearly total and its distribution did not vary so widely. Good crops 
have been grown in the area in years when precipitation totaled only 
slightly above 20 inches, and poor crops in years when it totaled 30 
inches or higher. The length and severity of droughts during periods 
critical for crop development are the strongest determinant of yield. 
Periods in which the weather favors lush growth of vegetation are 
frequently followed by prolonged drought and heat. Not only is the 
distribution of rainfall erratic, but characteristics of the soil limit the 
depth to which crops can feed regularly. The soil does not hold water 
readily available in such quantities that crops can escape injury by 
an extended period of drought or, when temperatures are extremely 
high, even a medium period of drought. Consequently the area is no 
less subject to drought losses than many having much less rainfall. 

The year 1949 offers a good illustration of how drought at a critical 
time can affect crop yields in southwestern Oklahoma. Precipitation 
was ample from early spring until late June, and crop prospects were 
excellent. Low precipitation in July and much of August changed a 
prospective bumper crop into a mediocre one, even though tempera- 
tures were a little below normal. 

Monthly and annual totals and averages for precipitation at the 
Lawton Field Station in 1916-49 are given in table 16, appendix. 

TEMPERATURES AND FROST-FREE PERIOD 

Temperatures at Lawton in the 34 years 1916-49 ranged from as 
high as 115° F. to as low as —9°. The yearly maxima have been 
equaled or exceeded by those at many other locations in the Great 
Plains. Summer temperatures usually were moderately high for a long 
period (table 17, appendix). In 1916-49 temperatures of 100° or 
more occurred repeatedly in every month from May through October. 
In the whole 34-year period the monthly maximum for July never fell 
short of 100° and that for August did so only once. The maxima for 
June and September reached or exceeded 100° in half the years. At 
Lawton a temperature of 100° or a little more is not oppressive when 
the humidity is below the local average. In July and August the 
monthly minimum temperature was usually 60° or higher and daily 
minima were generally in the higher sixties or low seventies. Unin- 
terrupted moderate to high temperatures are conducive to a lush 
growth of crops when moisture conditions are favorable, but such a 
growth generally becomes a handicap if favorable moisture conditions 
cease. 

The average frost-free period for the 33 years 1917-49 was 214 days, 
extending from April 2 to November 2 (table 18, appendix). Late 
maturing cotton is the only local crop likely to be injured by fall frosts. 
Spring frosts are not likely to injure field crops in the area but may 
damage fruit and truck crops. 

WIND VELOCITY 

Monthly average wind velocity was low except in March, when it 
was about 8 miles per hour, and in April, when it was about 7.5 miles 
per hour (table ]9, appendix). The prevailing wind during the 
growing season comes from the southwest. 



CROP ROTATION, TILLAGE, AXD FERTILITY EXPERIMENTS 5 

Wind velocity was measured with an anemometer exposed at a 
height of 2 feet above the ground, which approximates the height 
levels of field crops. 

EVAPORATION 

The evaporation at the Lawton station for the 6 months April- 
September averaged 45.29 inches and that for the 8 months April- 
November averaged 52.82 inches (table 20, appendix). Evaporation 
was low compared with that at any of the other dryland stations in 
the southern Great Plains but often was excessive; during drought 
periods it sometimes exceeded one-half inch in a single day. 

Evaporation was measured in a tank 6 feet in diameter and 24 
inches deep. The tank was sunk in the ground to a depth of 20 inches 
and was kept filled with water to about the ground level. 

SOIL CHARACTERISTICS 

The soil of the experimental area was classed as Lawton silt loam, 
a type representative of the heavy upland soils of southwestern 
Oklahoma. It was reddish-brown in color and had fairly good natural 
fertility. Soil depth on the area ranged from about 3 feet to more 
than 6 feet. »A layer of strongly weathered gravel mixed with clay 
and other fine material was found at depths ranging from less than 
1 foot to more than 3 feet. The location of this layer appeared to 
have little to do with crop growth; no difference in crop growth was 
observed between areas where gravelly material occurred at a depth 
of less than 18 inches and areas where the soil was free from gravel to 
a depth of 3 feet or more. The presence of the gravel layer did have 
the effect of making soil-moisture sampling so difficult and unreliable 
that attempts at soil-moisture determinations were discontinued after 
the first few seasons. 

No soil samples from the experimental area were analyzed before 
cropping was started, but samples from a virgin area having soil of the 
same type within a few hundred feet of the experimental area were 
analyzed in 1947. The average nitrogen and carbon contents of these 
samples are given in table 1, and the mechanical analysis, by depth, 
in table 21, appendix. It is believed that these samples represented 

Table 1. — Nitrogen and carbon content and carbon-nitrogen ratio of 
virgin Lawton silt loam x 



Depth (inches) 


Nitrogen 2 


Carbon 3 


C/N ratio 3 


0-6 

6-12 


Percent 
0. 158 
. 106 


Percent 
1. 94 
1. 13 


11.8 
11.2 







1 Samples were taken within a few hundred feet of the Lawton Field Station 
and were analyzed at the Northern Great Plains Field Station, Mandan, N. Dak. 

2 Average for 9 duplicate samples. 

3 Average for 3 duplicate samples. 



6 CIRCULAR 95 1, IT. S. DEPARTMENT OF AGRICULTURE 

the virgin condition of the soil of the experimental area rather accu- 
rately. The profile of the virgin Lawton silt loam analyzed was 
described 3 as follows: 
Lawton silt loam: Profile 470k 16-1 

In native pasture just north of Lawton Field Station on land belong- 
ing to the Indian Mission of the Reformed Church in America. 
Located in Comanche County, Okla., about 2 miles north of Lawton 
in SW 1/4 of SE 1/4 section 19, T. 2 N, R. 11 W. Samples collected 
from a pit by L. T. Alexander and E. H. Templin, April 28, 1947. 

Gently undulating prairie; lightly pastured; vegetation is largely of 
unidentified short and mid-grasses, probably including one or more 
gramas and buffalo grass. No Andropogons were seen but they may 
have been an important part of the vegetation before pasturing. 
The surface is freely drained, with gradient of about 1 percent, and 
weakly convex. 

Plant roots were present and comparatively numerous to the great- 
est depth examined, 61 inches. The soil was moist throughout (ap- 
proximately at field capacity) at the time of sampling, which was after 
a winter of about average rainfall. 

1. 0-6 inches, A h horizon. Brown (7.5YR 4/2; 2.5/2, moist) silt 
loam; strong fine granular; friable; noncalcareous. Sample 470k 
16-1-1 

2. 6-12 inches, Ai horizon. Brown (7.5YR 4/3; 3/3, moist) heavy 
silt loam; friable; strong fine granular; grades into horizon below. 
Sample 470k 16-1-2 

3. 12-15 inches, A 3 horizon. Reddish-brown (5YR 4/4; 3/3, moist) 
silty clay loam; very strong medium granular; noncalcareous; friable; 
grades below. Sample 470k 16-1-3 

4. 15-19 inches, Bi horizon. Reddish-brown (5YR 4/4; 3/4, moist) 
silty clay; friable; strong medium granular; grades below. Sample 
470k 16-1-4 

5. 19-30 inches, B 2 horizon. Reddish-brown (4 YR 3.5/4; 4/5, 
crushed; 3/4, moist uncrushed; 4/6, moist crushed) clay; firm; perme- 
able; compound moderate medium granular and medium prismatic; 
color is slightly variegated; passes into layer 6 through a 1-inch transi- 
tion. Sample 470k 16-1-5 

6. 30-35 inches, B 3 horizon. Partly weathered igneous pebbles in 
an equal volume of red (3YR 3/6) clay; granular; lower boundary 
sharp. Sample 470k 16-1-6 

7. 35-45 inches, Ci horizon. Red (3.5YR 3/5; 3/6, moist) clay; 
strongly prismatic; roots abundant in the crevices between prisms, 
outsides of prisms shiny; firm but slowly pervious; noncalcareous; 
grades below. Sample 470k 16-1-7 

8. 45-54 inches, C 2 horizon. Red (3YR 4/6, moist) sandy clay; 
friable to firm; strong coarse prismatic; exteriors of prisms are coated 
with dark-brown films; concretions of black crystalline minerals, 
probably magnetite (?), are abundant; grades through 2-inch transition 
to layer below. Sample 470k 16—1—8 



3 In a memorandum dated March 6, 1948, by E. H. Templin, who, with L. T. 
Alexander, had selected the sampling location. 



CROP ROTATION, TILLAGE, AXD FERTILITY EXPERIMENTS 7 

9. 54-61 inches, plus. C 3 horizon. Partly weathered waterworh 
igneous gravel in a matrix of noncalcareous clayey fine earth. Sample 
470k 16-1-9 

The soil of the experimental area was found to be pervious to water 
and roots to at least 5 feet; plant roots were found at the lowest depth 
reached, 61 inches. The high silt and clay content of the first 4 
feet of soil (table 21, appendix) no doubt retarded penetration of water 
and probably inhibited ready penetration of roots in times of sudden 
stress. 

CROP HAZARDS OTHER THAN THOSE OF CLIMATE 

PLANT DISEASES 

Plant diseases are an annual threat to crops in southwestern 
Oklahoma. 

Some of the major diseases of wheat, oats, and barley can be con- 
trolled by seed treatment. Diseases of small grains that can be con- 
trolled in this way include the smuts of wheat, oats, and barley and 
the stripe disease of barley. Those that have not been controlled 
satisfactorily by seed treatment include western dryland foot rot, 
leaf rust, and septoria on wheat and crown rust on oats. The breeding 
of resistant varieties offers the greatest promise of eventual control 
of these diseases. Stem rust in southwestern Oklahoma usually 
appears too late in the season to offer a serious problem. Winter 
barley in the area has been comparatively free from stripe rust, scab, 
and powdery mildew. 

Grain and forage sorghums and broomcorn are susceptible to dis- 
eases that often cause crop losses (19). These diseases (1) reduce 
the stand by rotting the seed or by killing the seedlings; (2) affect the 
leaves and reduce the value of the forage; (3) affect the heads and pre- 
vent normal grain development; and (4) involve rot of roots or stalk 
and prevent normal development and maturing of the plant. The 
outstanding importance of sorghums, which are grown for forage, 
grain, sirup, broom making, and a certain kind of starch, makes it 
very desirable to recognize these diseases and use'all possible means of 
control. 

Various seedborne and soil-inhabiting fungi do damage to sorghum 
particularly when the soil is cold and wet. Prompt germination of 
sorghum seed requires a soil temperature above 70° F. Control 
measures include careful selection of well matured and property cured 
seed. Before being planted, the seed should be dusted with some good 
disinfectant that will give protection from seedborne fungi and to 
some extent from harmful soil fungi. 

The three bacterial leaf diseases stripe, streak, and spot may 
occur wherever sorghum is grown, especially when moist weather with 
temperatures of 75° to 85° F. prevails. These diseases generally do 
not develop until the plants are nearing full growth, but they may 
spread over the leaves very rapidly, reducing the forage value of the 
crop and causing some shrinkage of the kernels. 

The three smuts of sorghum are covered kernel smut, loose kernel 
smut, and head smut. Control measures for the first two of these 
include seed treatment, use of smut-free seed only, and use of smut- 

305536 — 55 2 



8 



CIRCULAR 95 1, U. S. DEPARTMENT OF AGRICULTURE 



resistant varieties. At present, seed treatment is the most effective. 
Although head smut destroys the entire head, it is the least important 
of the three. Sanitation seems to be the one effective means of con- 
trolling it. 

Koot and stalk diseases of sorghum include pythium root rot (milo 
disease), weak neck, and several stalk rots. Practically all the grain 
sorghums grown commercially at the present time are resistant to 
root rot, but none of the commercial varieties or strains is free from 
charcoal rot of the stalks. Charcoal rot is characterized by a breaking 
over of the stalks (fig. 2). Weak neck is an important factor now that 
combine harvesting of sorghums has become prevalent. In weak 
neck the upper part of the stalk (peduncle) bends over and breaks, 





Figure 2. — A, Charcoal rot damage to susceptible variety of sorghum; B, re- 
sistant selection exhibiting no injury. 



CROP ROTATION, TILLAGE, AND FERTILITY EXPERIMENTS 9 

with the result that the head falls to the ground and is lost. Weak 
neck is not a parasitic disease; it is a characteristic of certain varie- 
ties — most of which are adapted to the Lawton area. The remedy is 
to grow varieties the stalks of which remain green for a considerable 
period after the grain ripens. Such varieties include Westland, Mid- 
land, and Kalo Selection H. C. 617. 

Bacterial blight, or angular leaf spot, is present on cotton in south- 
western Oklahoma nearly every year and has frequently almost de- 
foliated young cotton plants when they were 6 to 12 inches high. 
Progress has been made in controlling it by using disease-free seed, 
treating seed with organic mercury compounds, and developing re- 
sistant varieties. Wilt and cotton root rot cause considerable damage 
to cotton along the southern boundary of Oklahoma within 50 miles 
of Lawton. 

Detailed information on controlling crop diseases through seed 
treatment, cropping practices, or use of resistant crop varieties can 
be obtained from county agents or State agricultural experiment 
stations. 

DESTRUCTIVE INSECTS 

Insects injurious to crops have taken a heavy toll in southwestern 
Oklahoma, forcing control measures and changes in farm management 
practices. On the station they made necessary many changes in 
cropping practices ; they limited the numbers of crops and crop varie- 
ties that could be grown and influenced the time of planting and the 
field management of certain crops. 

Chinch bugs, greenbugs, army worms, wheat stem maggots, and 
grasshoppers all damage wheat, oats, and barley. Sorghum and corn 
are particularly subject to attacks by the chinch bug. This insect mi- 
grates to corn and sorghum when the small grains approach maturity 
and feeds on them the rest of the season. The damage usually be- 
comes more intense with each successive generation. The chinch bug 
has been the limiting factor in the production of many of the grain 
sorghums, such as milo, except on sandy land where the small grains 
are not grown. The abundant chinch bug population at Lawton 
made the station a desirable location for studying the biology of this 
insect and for breeding sorghums resistant to the chinch bug (fig. 3). 
Results of efforts along these lines have been reported in numerous 
publications (3, 4, 6-9, 11-15, 23, 29-32). 

Cotton is attacked by the bollworm, boll weevil, aphids, and pink 
bollworm. Alfalfa, also, is attacked by aphids. 

New and better insecticides and improved equipment for applying 
them promise more rapid and effective control than has heretofore 
been possible. Current recommendations on measures for controlling 
crop insects can be obtained from county agents, State agricultural 
experiment stations, and the United States Department of Agriculture. 

BIRD DAMAGE 

Constant precautions were required to protect the sorghums from 
bird damage. The many trees in the city of Lawton and along nearby 
Cache Creek furnish homes for many birds. These, together with 
flocks of migrating birds, created a serious problem at the station. 
Constant efforts to frighten the birds away reduced bird damage but 



10 



CIRCULAR 95 1, U. S. DEPARTMENT OF AGRICULTURE 




Figure 3. — Dwarf Yellow milo in the center row has been almost completely 
destroyed by chinch bugs. At the right is a chinch-bug-resistant hybrid of 
which Dwarf Yellow milo was one of the parents. 

did Dot eliminate it. Early maturing sorghum varieties, which be- 
come attractive to birds before the crops generally grown in the lo- 
cality do so, were often seriously damaged. Bird injury to varieties 
that mature later was less concentrated but nevertheless considerable. 
The grain yield of the sorghums grown in rotation experiments was 
reduced by birds in many years. This hazard applied more particu- 
larly to the station than it does to southwestern Oklahoma as a whole. 

SOIL EROSION 

Water erosion of the soil is serious in the Lawton area; wind erosion 
is of minor importance. The torrential character of many summer 
and fall rains and the slowly permeable nature of the soil combine to 
intensify runoff and the consequent erosion problem. Land where a 
clean cultivated crop is being grown is especially subject to abnormal 
erosion, and even the most approved methods of handling the land 
do not entirely protect it. 

Some soils, particularly on slopes, are so subject to erosion that only 
a return to a soil-binding crop such as grass can prevent their eventual 



CROP ROTATION, TILLAGE, AND FERTILITY EXPERIMENTS H 

impoverishment or destruction. All the soils require careful handling 
for control of erosion. 

On the station, erosion was most serious where cultivated crops were 
grown continuously or frequently and on some of the roads. A minor 
amount of sheet erosion took place on all the land. 

Information on methods of handling soil of various types to mini- 
mize erosion may be obtained from State agricultural experiment sta- 
tions or the Soil Conservation Service. 

PROCEDURE IN ROTATION AND TILLAGE EXPERIMENTS 

In the rotation and tillage experiments, plantings of each crop in 
any year were made with the same variety, usually one of the better 
adapted ones, with a view to excluding variables other than crop se- 
quence and tillage method. More productive and less productive 
cropping methods, respectively, were practiced on about half the plots 
of each of the crops kafir, cotton, wheat, and cowpeas. For other 
crops, the division was less even. 

Facilities of the station did not permit evaluating the different 
small-grain crops and varieties for grazing. 

Every combination of crop and tillage method in every rotation 
and tillage experiment was represented every year, on a Xo-acre plot. 
Thus each experiment occupied as many plots as there were years in 
the rotation. 

When the rotation and tillage experiments began, in 1916, all the 
rotations were tested on adjoining plots {21). For example, small 
grains, sorghums, and corn were grown side by side in the same field. 
It soon became evident that the proximity of small plots, by making 
it easy for chinch bugs to migrate between crops, intensified insect 
injury much beyond that occurring on farms. As a consequence the 
plan of work was revised in 1922 and 1923 so that all plots of corn and 
sorghum were in one field, designated field A, and all plots of small 
grain, except two oats plots, were in a separate field designated field 
B (fig. 4). Crops unattractive to chinch bugs, such as cotton and 
cowpeas, were grown in both fields. Soil amendments in the form of 
stable manure or of green manure were stressed in the experiments 
in field B. 

The rotations, and the tillage methods used in the rotation tests, 
were the following : i 

Field A: 

3-year rotations: 

No. 160. Kafir, kafir, cowpeas. All s. p. 

No. 161. Kafir, cowpeas, feterita. All f. p. 

No. 162. Kafir, cowpeas, feterita. All s. p. 

No. 163. Kafir, feterita, cowpeas. All f. p. 

No. 165. Kafir (f. p.), fallow, feterita. 

No. 166. Cotton (disked), feterita (s. p.), cowpeas (s. p.). 

No. 167. Cotton (disked), kafir (s. p.), cowpeas (s. p.). 

No. 168. Feterita (f. p.), fallow, kafir. 

No. 169. Feterita, cowpeas, kafir. All s. p. 

No. 205. Cotton (f. p.), cowpeas (f. p., plowed under), feterita. 



4 S. p. = spring plowed. F. p. = fall plowed. S. clover=sweetcloyer. "Top- 
dressed," here and elsewhere in this publication, means topdressed with manure. 



12 CIRCULAR 951, TJ. S. DEPARTMENT OF AGRICULTURE 



**££&. 




Figure 4. — Aerial view of the Lawton Field Station. Field A appears in the 
right foreground, field B in the right center. The road at the right of field B 
is a station boundary. 

4-year rotations: 

Xo. 133. S. clover, s. clover, cotton (f. p.), cowpeas (f. p.). 

Xo. 134. S. clover, s. clover, cotton (f. p.). kafir (lister planted . 

Xo. 274. Kafir (s. p.), sorgo (drilled, f. p.), corn (f. p.), cotton (f. p.). 

No. 275. Cotton (f. p.), cotton (f. p.), kafir (s. p.), sorgo (drilled, f. p.). 

Xo. 276. Cotton, oats, kafir (manured), cowpeas. All f . p. 
6-year rotation: Xo. 142. Alfalfa, alfalfa, alfalfa, oats (f. p.), corn (s. p.), 
cotton is. p.). . 

Field B: 

2-year rotations: 

X'o. 260. Wheat (disked), cotton (s. p.). 
Wheat (f. p.), oats (f. p.). 
Wheat (f. p.), oats (disked). 
Wheat (f. p.), spring barley (disked). 
Wheat (disked), cowpeas (s. p.). 

Wheat on cowpea green manure, cowpeas (s. p., plowed under). 
Wheat, fallow. 
Wheat, fallow (manured). 
Wheat (topdressed), fallow. 
Wheat (topdressed\ cowpeas (s. p.). 
Cotton, rye (plowed under). 
Cotton' (f. p.), oats (disked , 
Cotton (f. p.), wheat (disked . 
Cotton (s. p.), peanuts or Mung beans (s. p.). 
Cotton (s. p. and topdressed), cowpeas (s. p.). 
Cotton (s. p.), cowpeas (s. p.). 

Cotton on cowpea green manure, cowpeas (s. p., plowed under). 
Cotton, fallow. 
Cotton, fallow (manured). 
Cotton (topdressed), fallow. 



Xo. 


261. 


Xo. 


262. 


Xo. 


264. 


Xo. 


265. 


Xo. 


266. 


Xo. 


267. 


Xo. 


268. 


No. 


269. 


Xo. 


364. 


Xo. 


390. 


Xo. 


391. 


Xo. 


392. 


Xo. 


393. 


Xo. 


394. 


Xo. 


395. 


Xo. 


396. 


Xo. 


397. 


Xo. 


398. 


Xo. 


399. 



CROP ROTATION, TILLAGE, AND FERTILITY EXPERIMENTS 13 

3-year rotations: 

No. 195. Cotton (f. p.), cotton (f. p.), wheat. 

No. 196. Cotton (f. p.), cowpeas (f. p.), winter barley. 

No. 197. Cotton (f. p.), wheat, wheat (f. p.). 

No. 198. Cotton (f. p. and topdressed), cotton (f. p.), wheat. 

No. 199. Cotton (f. p.), cowpeas (plowed under), wheat. 

No. 200. Cotton (s. p.), cowpeas (s. p.), wheat. 

No. 201. Cotton (f. p.), cowpeas, (f. p.), spring barley. 

No. 202. Wheat, cowpeas (plowed under), cotton. 

No. 203. Cotton (f. p.), cowpeas (f. p.), wheat. 

No. 204. Cotton (f. p.), wheat (topdressed), wheat (f. p.). 

Continuous and alternate cropping with cotton, kafir, sorgo, corn, 
and feterita by different tillage methods was practiced on field A. 
Continuous cropping with wheat by different tillage methods was 
practiced on field B. In the tillage experiments with wheat, the 
tillage necessary to control weeds was given to all the plots from the 
time tillage began until seeding time. All row crops were kept sub- 
stantially free from weeds. 

Peanuts were grown in rotation with cotton in 1924-42. Mung 
beans were grown as a hay crop in rotation with cotton in 1943-49. 
Broomcorn was grown in 1917-33. 

Castor beans and flax were grown for a number of years on the 
station but not in tillage tests. 

The varieties of principal crops grown in the rotation and tillage 
experiments and the years in which they were grown are as follows: 

Cotton: Acala and improved strains of Acala 1924-49. 

Wheat: 

Turkey Red 1924-26, 1928-45. 

Kanred 1927. 

Comanche_ 1946-49. 

Kafir: 

Reed 1924-39, 1942-48. 

Sharon 1940, 1949. 

Feterita: 

Dwarf 1924-26. 

Spur 1927-45. 

Kafirita 1946-49. 

Sorgo: Sumac 1924-49. 

Corn: 

Silvermine 1924. 

Surecropper 1925. 

Bloodv Butcher 1926-30. 

White June 1931. 

Hays Golden 1932-49. 

Cowpeas: 

Blackeve___ __ __ 1934, 1936-42, 1946-49. 

Early Buff 1924-28. 

Chinese White 1929-32, 1943. 

Brown Crowder - 1933. 

Texas Velvet Pod 1935. 

New Era 1944-45. 

Spring Barley: 

Common 1924-25. 

Manchuria 1926-39. 

Wintex 1 1940-44. 

Tenkow 1945-49. 

Winter barlev: 

Wisconsin. . 1924-45. 

Tenkow 1946-49. 



14 CIRCULAR 951, U. S. DEPARTMENT OF AGRICULTURE 

Spring oats: 

Fulghum 1 1924-43. 

New Nortex 1944-48. 

Fultex 1949. 

Alfalfa: Oklahoma Common 1924-49. 

Sweetclover: 

Common White 1924-31. 

Madrid Yellow 1932-49. 

YIELDS AND RELATIVE ADAPTATION OF CROPS 

Two crop-yield factors of particular importance are total production 
and dependability of production. These are indicated by the average 
yields and the annual yields (table 2). 

Cotton, with an average acre yield of 229 pounds of lint and 377 
pounds of seed, was one of the most dependable crops. It never failed 
completely, and its yield seldom averaged extremely low. Cotton 
occupied about one-third of the cultivated acreage during the first 40 
years of farming in southwestern Oklahoma. This acreage has since 
been greatly reduced for reasons other than relative adaptation. 

Winter wheat likewise performed dependably. Its only complete 
failure occurred in 1946, when the crop was destroyed by greenbugs. 
Largely because of the crop's value for grazing and its relatively high 
average yield of 15.1 bushels to the acre, wheat acreage has shown a 
marked increase. Improved varieties and, more particularly, im- 
proved equipment and methods of production have contributed to 
this increase. 

Oats are another dependable small grain, the popularity of which as 
a crop has been greatly enhanced by new winter-hardy varieties. No 
winter oats were grown in the rotations, but variety trials (27) have 
shown them to be much more dependable and productive than spring- 
sown oats. They have largely replaced ths latter on farms in south- 
western Oklahoma. Winter oats have numerous advantages, includ- 
ing production of winter and early-spring pasture, less rust damage 
(because of early maturity), less erosion during the winter months, 
and less damage from late-spring freezes and from insects. 

Winter barley is fairly well adapted to the climate of southwestern 
Oklahoma, but its production has been held to a minor place by green- 
bugs (1), chinch bugs, and fungus diseases. If these were controlled, 
winter barley would have place as a pasture crop — for farm animals, 
like insects, exhibit a marked preference for it. 

The grain and forage sorghums, which have long been dependable 
producers of feed and cash income, have become still more valuable in 
recent years because of spectacular improvement. Development of 
grain sorghum varieties that can be harvested with a combine has 
eliminated much of the labor connected with harvesting and has 
consequently reduced production costs. Forage sorghums have been 
improved in palatability. At present, in southwestern Oklahoma, 
most sorghums grown for grain are of a combine type and sweet 
sorghums (sorgos) are grown for forage. The varieties grown in the 
rotation tests are not necessarily the ones of most importance today, 
but they give a good picture of the dependability of the best varieties. 

Kafir is a good representative of the dual-purpose sorghums. Both 
its forage and its grain are of excellent quality. No complete failure 
of kafir stover occurred in the experiments. The grain yields tabulated 



CROP ROTATION, TILLAGE, AND FERTILITY EXPERIMENTS 15 



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16 CIRCULAR 9 51, U. S. DEPARTMENT OF AGRICULTURE 

do not truly reflect the production that should be attained in south- 
western Oklahoma. Planting on the station had to be done earlier 
than is best for the crop, in order to reduce chinch bug damage. The 
early planting caused kafir to ripen earlier on the station than it does 
generally in southwestern Oklahoma, and this resulted in greater bird 
damage. In some years, birds completed the grain failure of drought- 
injured kafir crops. Most kafir grain failures are due not to a single 
cause but to a combination of drought with insect or bird damage or 
with disease. The increased use of combine-type sorghums has 
reduced the acreage of kafir varieties such as Keed and Sharon. 

Feterita has been of some importance in southwestern Oklahoma as 
a catch crop, but its grain yield averages lower than that of kafir and 
its stover is much less palatable. In recent years it has been almost 
completely replaced in the area by feterita-kafir hybrids, such as 
kafirita, that are much less susceptible to the chinch bug. 

Sorgo (of the Sumac variety) produced consistently good yields of 
fodder, averaging nearly 3 tons of air-dry material to the acre. In 
only 1 of the 26 years did the yield fall below a ton to the acre. Sorgo's 
total grain and stover yield was nearly 50 percent higher than that of 
kafir. Sorgo planted with a grain drill produced an average yield of 
more than 4.5 tons to the acre. In comparison with sorgo in culti- 
vated rows it yielded much more forage, in productive years. 

The fact that alfalfa, although highly important on creek and river 
bottom lands in southwestern Oklahoma, has not gained favor on the 
uplands can be attributed to the general undependability of its pro- 
duction and its prevailingly poor first-year production. The fair 
yield averages of alfalfa in the second and third years after planting 
on the station plots — more than % ton per acre— resulted from very 
good yields in a few years rather than from fair yields each year. 
Second- or third-year yield amounted to less than 1,000 pounds to the 
acre in nearly one-third of the instances. Newly planted alfalfa 
produced a measurable crop in only 8 of the 26 years. 

Cowpeas (fig. 5) were the most dependable source of legume hay on 
the heavy soil of the station. The acre yield of cowpea hay on the 
plots averaged more than a ton for the study period and fell below 
1,000 pounds in only 1 year. 

The sweetclover yield data do not cover all the time that sweet- 
clover was grown at the Lawton station. Prior to 1933, however, 
the seed was sown broadcast and the crop failed more often than it 
succeeded. From 1933 onward, sweetclover was grown in paired 
cultivated rows and good stands were obtained except in the severe 
drought years of the early thirties. On the rotation plots sweetclover 
was harvested for hay. A good yield — or, in fact, a yield of any 
kind — was seldom obtained in the year of seeding. Second-year pro- 
duction was fairly good. Elsewhere on the station, good yields of 
sweetclover seed w^ere obtained frequently. The seed was harvested 
with a row binder (fig. 6), The same method can be used for sweet- 
clover hay. It eliminates the dirt contamination that takes place 
when sweetclover in cultivated rows is harvested with regular haying 
equipment. 

The grain yield of corn exceeded that of kafir somewhat, but part 
of the excess was due to freedom from bird damage. The acre yields 
do not tell the whole story. In more than half the years the grain 



CROP ROTATION, TILLAGE, AND FERTILITY EXPERIMENTS 17 




Figure 5. — Chinese White cowpeas (station strain) growing on the Lawton 
Field Station. This crop produced, on an average, more than a ton of hay 
per acre. 



£':«vA& 



l-^IS i v 




::^" . *: 



Figure 6. — Using a row binder to harvest sweetclover, grown in paired cultivated 

rows, for seed. 

was of poor or very poor quality. Stover yields were low in compari- 
son with those of sorghum, and in a number of years the corn stover 
was worthless. Corn does not compare well with sorghums for all- 
around use on the tight upland soils. 



18 



CIRCULAR 951, IT. S. DEPARTMENT OF AGRICULTURE 



Good peanut crops were obtained occasionally, but in more than 
half the years the crop failed, frequently because of damage by rabbits. 
The hay yield of Mung beans averaged about 260 pounds per acre 
lower than that of cowpeas during the same period. For broomcorn, 
failures were frequent and average brush yields low. Castor bean 
and flax data are too few to merit discussion. 

TILLAGE AND SEQUENCE RESULTS 
WINTER WHEAT 

Tillage Results 

Winter -wheat yields (fig. 7) were higher on plots that were tilled as 
soon as practicable after harvest than on comparable plots where tillage 
began shortly before seeding. They were somewhat higher where 
tillage loosened all the soil to a depth of about 8 inches than where it 
affected a shallower layer or loosened only a part of the tilled layer. 



YIELD (BUSHELS) 

10 20 



METHOD 



Early plowed 4 inches 



Early plowed 8 inches 

Early plowecj 8 inches and subsoiled 
10*12 inches additional 

Early disked 



Early listed or basin listed 

Early listed or basin listed 
and manured 



Early plowed (in alternate years ) 
Early disked (in alternate years) 

Late plowed 4 inches 
Late disked 



Figure 7. — Average acre winter wheat yields obtained with various kinds of 
seedbed preparation at the Lawton Field Station in 1924-49. Early tillage 
was performed as soon after harvest as practicable; late tillage began shortly 
before seeding. The plowed and subsoiled plot was thus tilled for 2 consecutive 
years, then was plowed only for 2 years. The plots disked in alternate years 
were the same that were plowed in alternate years. 




CROP ROTATION, TILLAGE, AXD FERTILITY EXPERIMENTS 19 

A plot disked early in each year produced an average wheat yield fal- 
low er than that of any other early tilled plot and 4 bushels per acre 
lower than that of a plot early plowed to a depth of 8 inches. On two 
plots on which early disking and early plowing were practiced in 
alternate years, slightly smaller average yields were produced after 
disking than after plowing. 

Subsoiling, which followed 8-inch plowing on 1 plot in alternate 
pairs of years and loosened the soil to an additional depth of 10 to 12 
inches, did not lead to a higher yield of wheat than plowing to normal 
depth only; if there was a measurable difference, it was unfavorable 
to subsoiling. The subsoiled plot's average acre yield in the 14 years 
in which it was thus tilled failed by 1 bushel to match that of a plot on 
which 8-inch plowing only was practiced every year. Its average 
acre yield in the 12 years in which 8-inch plowing was practiced at a 
1- or 2-year interval after subsoiling was 0.2 bushel lower than that of 
the continuously plowed plot. Evidently there is no immediate or 
residual benefit to wheat from subsoiling. 

The two winter wheat plots that were listed produced somewhat 
lower yields than those that were plowed. The 26-year averages of 
wheat yield for these plots do not indicate that the manure applied 
to one of them gave any benefit. The detailed data (table 22, appen- 
dix) indicate, however, that eventually it did. During the first 
half of the 26-year period, wheat yields on the manured listed plot 
were lower than those on the unmanured one in 8 of the 13 years and 
averaged 1.7 bushels per acre lower; but during the second 13 years, 
the manured plot produced the lower yield only 4 times and its 
average acre yield was the higher by 1.1 bushels. Evidently its 
soil had reached a condition in which manure was helpful rather 
than harmful to grain yields. Straw yields were higher on the ma- 
nured land throughout the experiment. The yield trends of the two 
plots were not regular, but the relation of the yield curves underwent 
a gradual change that is not wholly obscured by seasonal differ- 
ence (fig. 8). 

Results from the wheat studies indicate that timeliness of tillage 
has a great influence on yield. 

Weed control during the period between harvest and seeding prob- 
ably is the chief benefit from tillage commencing soon after harvest, 
but there is some evidence that the loosening of the soil to a depth 
of several inches may be beneficial, also. In tins case most of the 
tests were made with the plow, but it is believed that any other 
implement loosening the soil to the same depth and controlling weeds 
equally well would be equally effective. 

Results of tillage tests with wheat are given in detail in table 22, 
appendix. 

Sequence Results 

Wheat was grown in combination with cotton, small grains, cow- 
peas, and fallow in a number of 2-year and 3-year rotations. Barn- 
yard manure and cowpea green manure were used in some wheat 
rotations. 

Wheat was less productive after cotton than after small grain, but 
manuring the cotton land eliminated most of the difference (table 3). 



20 



CIRCULAR 951. TJ. S. DEPARTMENT OF AGRICULTURE 



20 





il 
11 










l BUSHELS 


■ \ 1 

: W 


H 




A v /A 


3 10 

UJ 

> 






% 


J 1 
/l 

[J 




5 






-MANURED 


















• NOT MANURED 














i 


, . 1 . 


J i 1 1 1 1 1 i. 


1 


L 1 . i L-J 1 L_ 



1928 



1933 



1938 



1943 



1948 



Figure 8. — Five-year moving yield averages of manured and unmanured 
continuous wheat at Lawton, Okla., 1924-49. The value charted for each 
year is the average annual acre yield for the 5-year period ending with that 
vear. 



Wheat after cowpeas removed as hay was approximately equal in 
yield to wheat after small grain. Manured wheat after cowpeas 
removed as hay was about equal in yield to wheat after cowpeas 
plowed under. 

Wheat produced its highest yields on fallow. On unmanured fallow 
it produced an average grain yield more than a bushel to the acre 
higher than that on cowpea green manure, although the straw yields 
were nearly the same. On manured fallow it produced 2 bushels 
per acre more grain than on unmanured fallow, and 500 pounds per 
acre more straw. 

The high yield on fallowed land does not mean that fallowing is 
profitable as a general practice in growing wheat in southwestern 
Oklahoma. A given acreage of land cropped continuously to wheat 
by good production methods will produce, on an average, about 6 
bushels more of grain to the acre annually than the same acreage 
half in fallow and half in wheat on fallow. Fallowing may justifi- 
ably be practiced in the area as a preparation for wheat in order to 



CROP ROTATION, TILLAGE, AX'D FERTILITY EXPERIMENTS 21 

Table 3. — Yields of winter wheat grown in different sequences by dif- 
ferent cropping methods at Laivton, Okla., 192^-^9 



Preceding crop, and cropping practice 


Plots 


Average acre yield 


Grain 


Straw l 


Cotton: 

Stubbled in 

Stubbled in and manured 

Small grain, early plowed 

Cowpea hay: 

Disked 

Disked and manured 

Cowpeas, plowed under 


Nu ruber 
5 
2 
5 

3 
1 

2 

1 

2 


Bushels 
13.4 
15. 1 
15. 7 

15. 9 
18. 

18. 1 

19. 4 
21. 7 


Pounds 
1,441 
1,610 
1, 754 

1,657 
1,952 
1, 989 


Summer fallow: 

Xot manured 

Manured 


1, 993 

2, 514 











1 Xot harvested after 1946. 

produce seed free from mixtures (fig. 9), under special conditions 
such as after failure of a wheat crop, or sometimes when wheat is 
to follow sorghum. Although wheat was not grown in rotation with 
sorghum in these studies, because of chinch bugs, it is known that 
yields of wheat are materially lower after sorghum than after cotton. 
Green manuring with cowpeas cost more than fallowing and con- 
tributed less to grain yield of wheat. It could be justified only if it 
maintained the productive capacity of the soil at a level higher than 
that of soil on which wheat is grown each year. Results presented 
later under the heading "Nitrogen Content of Cropped Soil" do not 
indicate that it does this. 





■■■-.. 

Figure 9. — Winter wheat growing on fallowed land at the Lawton Field 
Station, in a variety test. Fallowing, unprofitable as a general practice, is 
justified under special conditions such as need to prevent seed mixtures. 



22 CIRCULAR 951, U. S. DEPARTMENT OF AGRICULTURE 

The suitability of other crops for rotation with wheat depends on 
their own value and on how their yields are affected by wheat, as 
well as on their effect on wheat. Thus the relatively low yield of 
wheat after cotton does not necessarily mean that wheat should not 
be grown in that sequence. It does indicate that the value of a 
cotton crop preceding wheat must be enough greater than that of 
a competing crop to compensate any reduction the cotton will cause 
in the wheat yield. 

Results of rotation tests with wheat are given in detail in table 
23, appendix. 

COTTON 

Cotton yields obtained with different types of tillage and different 
rotations are presented in terms of weight of seed cotton, or total 
weight of lint and seed. Weight of seed cotton is as reliable a means 
of comparing treatments as the separate weights of lint and seed 
would be. The average proportion of lint varied from year to year 
(table 2), but differences in lint percentage in a given year according 
to treatment were so small that measuring the lint for each treatment 
probably would have resulted in a greater error than computing a 
percentage for the whole crop and assigning this percentage to each 
treatment, 

Tillage Results 

The cotton yields in 1917-31 for the seven cropping methods then 
in use (table 4) show a superiority of winter over spring plowing, a 
possibility of additional benefit from subsoiling, lack of a material 
response to summer fallowing, and a very much lower yield from land 
listed in the winter or spring and lister planted than from plowed land. 
Land winter plowed and lister planted produced cotton yields not 
much below those on land winter plowed and surface planted, 
seems certain that the low yields on land that was listed instead 
of being plowed were due to failure to loosen the soil deeply well in 
advance of planting. 

Because of the unexpectedly poor cotton yields from listed land in 
1917-31, the lister treatments were tested again, in duplicate, with 
others for comparison, on another piece of land in 1933-49. Results 
from the second test (table 4) confirm, in the main, those of the first. 
Winter-listed and lister-planted land produced cotton yields more 
than 200 pounds to the acre below those on winter-plowed and lister- 
planted land. Delaying the initial listing until spring and then lister 
planting led to a slightly lower yield. Results from the second test 
do not indicate any benefit from subsoiling. 

Results of tillage tests with cotton are given in detail in table 24, 
appendix. 

Sequence Results 

Cotton yields on fall-plowed cotton, sweetclover, corn, sorgo, and 
feterita land in field A were substantially the same (table 5). The 
yield on fall-plowed cowpea stubble exceeded the others materially, 
but how much of the difference was due to the previous crop and how 
much to manure in the rotation is a question. The lowest of the 



CROP ROTATION, TILLAGE, AND FERTILITY EXPERIMENTS 23 

Table 4. — Yields of cotton grown continuously by (liferent tillage 
methods and alternated with fallow in 1917-81 and comparable yields 
of cotton grown on other plots in 1933-49 at Lawton, Okla. 



Cropping method 



Continuous methods : 

Spring plowed, surface planted 

Winter plowed, surface planted 

Winter plowed and subsoiled, surface 
planted 

Winter listed, lister planted " 

Spring listed, lister planted 

Winter plowed, lister planted 

Alternately cropped and fallowed 



Average acre yield of seed cotton 



1917-31 



Pounds 
601 
655 

671 
485 
425 

629 

678 



1933-49 



On dupli- 
cate plots 



Pounds 



569 
628 
381 
412 
366 
385 
622 
604 



Aveiage 



Pounds 



599 
397 
376 
613 



1 None of these had been used in 1917-31. 

cotton yields in field A was that produced on disked cowpea stubble. 
This result does not indicate the influence of cowpeas on subsequent 
cotton yields; like results in the tillage tests, it indicates the necessity 
of loosening the soil mass deeply before planting cotton. 

Cotton yield was a little lower on spring-plowed corn ground than 
on fall-plowed corn ground — in spite of the fact that the rotation in 
which the spring plowing occurred contained alfalfa, which would be 
expected to provide a better state of fertility. This difference between 
results on spring-plowed and fall-plowed ground corresponds to results 
in the tillage tests. 

In field B, under comparable conditions cotton after wheat produced 
slightly higher average yields than cotton after cotton. In both 
3-year rotations of wheat, cotton, cotton, the cotton immediately 
following wheat was slightly more productive than the second cotton 
crop. 

Although tillage variables prevent exact comparisons, it seems 
evident that cowpeas were superior to wheat as a preparation for 
cotton. There is evidence that the same thing was true of oats. 
Yield of cotton averaged much lower after barley than after wheat, 
for some unknown reason. Yield of cotton after wheat on spring- 
plowed land equaled that on comparable fall-plowed land. This was 
one of few instances at Lawton in which yield after spring plowing 
equaled yield after fall plowing. 

Cotton yields on green-manured and on fallowed land were higher 
than those on land where a crop had been grown and harvested in 
the preceding year, but not enough higher to compensate the lack of 
a year's harvest. 



305536—55- 



24 



CIRCULAR 95 1, U. S. DEPARTMENT OF AGRICULTURE 



Table 5. — Yields of cotton grown in different sequences by different 
cropping methods at Lawton. Ok! a., 1924-49 





Field A 










treatment 


Average acre yield of seed cotton, 
by cropping method 


Preceding crop, and manuring 


Fall or 
winter 
plowed 


bprmg 

plowed 


Disked, 
fallowed, 
or green 
manured 


Cotton 


Pcunds 
675 
663 
673 
691 
689 


Pounds 


Pounds 


Sweetclover 






Corn 




i 641 




Sore;o 




Feterita 






Cowpeas 




2 598 


Cowpeas, manure in rotation 




764 










1 


Field B 


Wheat 


550 
591 
524 
572 


576 




Wheat, manure or green manure 
Cotton 


in rotation. 








Cotton, manure in rotation 






Cowpeas 


619 
635 




Cowpeas, manure in rotation 






Cowpeas, plowed under 




666 


Barlev 




503 

618 






Oats 






Peanuts or Mung beans 3 


597 




Rye. plowed under 




720 


Fallow 






690 


Fallow, manured 






799 


Fallow (cotton topdressed) 






706 











1 The rotation included alfalfa. 

2 Disked. 

3 Peanuts in 1924-42, Mung beans in 1943-49. 

In comparable rotations with and without manure, the higher cotton 
yields were produced on manured land. A difference in cotton yield 
was associated with difference in time of application of manure in the 
fallow rotations. Applying the manure when the land is being 
fallowed evidently results in much greater benefit than applying it as 
a topdressing after the cotton is planted. 

Results of rotation tests with cotton are given in detail in table 25. 
appendix. 

SORGHUMS 



Tillage Results 

Kafir, feterita, and sorgo yields (table 6) were higher on land that 
had been fall or winter plowed than on land that had been spring 



CROP ROTATION, TILLAGE, AND FERTILITY EXPERIMENTS 25 

plowed, where no soil amendment was involved. The stover yields 
on land that had been fall or winter plowed and subsoiled were higher 
than those on land that had been fall or winter plowed only, but 
certainly not enough higher to compensate the cost of subsoiling. 

Kafir that was lister planted produced materially smaller yields of 
grain than kafir grown on spring-plowed land, but it did not produce 
smaller yields of stover. 

Kafir and sorgo grew much more vigorously on plots that were 
manured in advance of spring plowing than on unmanured spring- 
plowed land. The greater growth resulted in greater yield of stover, 
but not in a materially greater yield of grain. In many years, the 
manured sorghum plots fired severely earlier than the others. 

Table 6. — Yields of kafir, feterita, and sorgo grown continuously by 
different cropping methods and alternated with fallow at Lawton, 
Okla., 1924-49 





Average acre yield 


Cropping method 


Kafir 


Feterita 


Sorgo 


> 


Grain 


Stover 


Grain 


Stover 


Continuous methods: 

Spring plowed 

Spring plowed and ma- 
nured 


Bushels 
14. 3 

14. 5 
16. 2 

16. 6 
11. 5 

19. 2 


Pounds 
2,900 

4, 176 
3, 109 

3,425 

2, 962 

4,019 


Bushels 
12. 4 


Pounds 
2, 294 


Pounds 
4, 719 

8,666 


Fall or winter plowed 

Fall or winter plowed and 
subsoiled 


13. 8 


2,531 


4, 927 

5, 978 


Lister planted 






5,266 


Alternately cropped and fal- 
lowed 


15. 9 


2,988 


6, 777 









Fallowing led to the highest yields of kafir and feterita and the 
second-highest yield of sorgo, but none of the yields on fallowed land 
were enough higher than those on plowed land to justify the sacrifice 
of a year's crop. 

Because of the low yields of kafir on listed land in the early years, 
tests were made to determine whether some variant of lister prepara- 
tion would give materially better results than others. The eight 
methods tested varied as*^ to time of beginning preparation, tillage 
after listing, and whether the kafir was planted in the original furrows 
or by splitting ridges. No tillage variant increased kafir yield above 
the level attained on listed plots in the original tillage experiments; a 
cropping variant including a winter application of manure, however, 
led to a'grain vield greater by more than 2 bushels to the acre and a 
stover yield about 800 pounds to the acre greater than that produced 
by a comparable listed plot not receiving manure. 

Results of tillage tests with sorghum are given in detail in tables 26, 
27, and 28, appendix. 



26 



CIRCULAR 951, U. S. DEPARTMENT OF AGRICULTURE 



Sequence Results 

Yields of kafir and feterita (table 7) did not vary greatly according 
to the preceding crop. The yield of kafir was not markedly increased 
by fallowing. The yield of feterita on green-manured land was 3 
bushels to the acre above that on fall plowing after harvested cow- 
peas — an increase much too small to justify the sacrifice of a harvest. 

The tillage results for both kafir and feterita in rotations agreed 
fairly well with those obtained in the regular tillage experiments. 
Fall or winter plowing led to greater yields than spring plowing. 
Kafir produced its lowest grain yield in the one rotation in which it 
was planted with a lister. The lister-planted kafir produced a rela- 
tively good stover yield, perhaps because of sweetclover in the 
rotation. 

Kafir on manured kafir land produced a lower grain yield but a 
slightly higher stover yield than that on comparable unmanured land. 
The lower average of grain yield on manured land in this instance was 
due chiefly to the crop of a single year. 1941. In that year early 
injury on manured land drastically reduced yield even though the 
season later became very favorable. 

Results of rotation studies with sorghum are given in detail in 
tables 28 and 29, appendix. 



Table 7. — Yields of kafir and feterita grown in different sequences by 
different cropping methods at Lawton, Okla., 1921^.-1$ 





Average acre yield, 


by cropping method 


Crop, preceding 
crop, and 
manuring 
treatment 


Spring 
plowed 


Fall or winter 
plowed 


Listed 


Fallowed or 
green manured 




Grain 


Stover 


Grai n 


Stover 


Grain 


Stover 


Grain 


Stover 


Kafir: 

Kafir 


Bushels 
| 12. 8 


Pounds 
2,830 


Bushels 


Pounds 


Bushels 


Pounds 


Bushels 


Pounds 


15. 6 

14. 

15. 


3, 382 
3, 538 
3, 191 










Kafir, manured- 














Feterita 


13.0 
13. 3 


3, 109 
3, 056 










Cotton 










Cotton, sweet- 
clover in 
rotation 






12. 2 


3, 472 






Cowpeas 

Oats, manured 


14. 


3,089 


15. 5 

16. 1 


3, 534 
3,556 














Fallow 










15.3 


3, 340 


Feterita: 
Kafir 


10. 9 

11. 5 


2,490 
2,425 


13. 3 
15. 1 


2, 696 
3,042 








Cowpeas 

Cowpeas, 

plowed 

under 














18. 1 


3, 218 


Cotton 


9. 9 


2, 397 



























CROP ROTATION, TILLAGE, AND FERTILITY EXPERIMENTS 27 

COWPEAS 

Results with cowpeas (table 8) emphasize the superiority of fall 
over spring plowing. Manure applied to another crop in the rotation 
increased cowpea hay production slightly. There appeared to be 
some residual benefit from sweetclover, also. 

Table 8. — Hay yields of cowpeas grown in different sequences by different 
cropping methods at Lawton, Okla., 192/+-49 



Field, preceding crop, and manuring treatment 


Average acre hay yield, by 
tillage method 


Spring 
plowed 


Fall or winter 
plowed 


Field A: 

Kafir 

Kafir, manured 


Pounds 

1, 976 




Pounds 

2, 241 
2, 629 


Feterita 

Cotton, sweetclover in rotation 


1, 965 


2, 127 
2, 443 


Field B: 
Wheat 


1, 917 

1, 961 

2, 140 




Cotton. _ J 

Cotton, manure in rotation 


2,066 







CORN 

Some results of the corn tillage experiments (table 9) contrast 
strikingly with results of experiments with other crops. No evidence 
appeared of superiority of fall plowing over spring plowing. Instead 
of a lower yield, lister planting without plowing led to a distinctly 
higher yield of grain. These differences may be explained by the fact 
that corn is more subject to firing from drought than most of the crops 
tested and often is actually benefited by the reduction of early growth 
resulting from listing. This has been observed not only at Lawton 
but also at other stations in the southern Great Plains. 

A result that has not been observed at other Great Plains stations 
is the response of corn to subsoiling. Yields following subsoiling were 
consistently high, averaging higher than those on fallow. This is the 
most substantial benefit to a crop from subsoiling that has been noted 
in the Great Plains. 

Yields on fallow land were much greater than those following spring 
or fall plowing where manure had not been used, but averaged little 
greater than those following listing. Fallowing cannot be recom- 
mended for corn production. 

The most striking result is the increasing response of the corn crop 
to manure (fig. 10). There was always some response to manure, 
but the yield difference between unmanured and manured land 
appeared to increase gradually. After the middle twenties, corn grain 
yields on unmanured land were maintained or increased but stover 
yields suffered a gradual decline. On manured land both grain and 
stover yields increased during the same period and grain yields from 
1941 onward exceeded those obtained when the land was first cropped. 



28 CIRCULAR 951, IT. S. DEPARTMENT OF AGRICULTURE 

40h 




1921 



1926 



1931 



1936 



1941 



1946 1949 



Figure 10. — Five-year moving averages of corn grain and stover yields per acre on 
manured and unmanured plots at Lawton, Okla. 



Table 9. — Yields of corn grown in different sequences by different 
cropping methods at Lawton, Okla , 192^-^9 



Preceding crop, and cropping method 



Average acre vield 



Grain 



Stover 



Corn: 

Spring plowed . 

Spring plowed, corn topdressed 

Fall or winter plowed 

Fall or winter plowed and subsoiled 

Lister planted 

Early cultivated, lister planted 

Oats, spring plowed l 

Sorgo, fall or winter plowed 

Fallow 

1 Alfalfa in rotation. 



lels 


Pounds 


16. 1 


1,253 


27. 4 


2,438 


16. 2 


1,280 


23. 6 


1, 721 


19. 6 


1, 376 


21. 9 


1, 570 


15. 1 


1, 660 


13. 6 


1, 510 


21. 9 


1, 652 



CROP ROTATION, TILLAGE. AXD FERTILITY EXPERIMENTS 29 

Grain yields of corn in certain late years of the experimental period, 
particularly on manured laud, were more reliable than grain yields of 
sorghums. This result is in sharp contrast with early experience at 
the station. It does not indicate that corn should replace sorghums 
in southwestern Oklahoma, for the crop is still plagued in the area 
by poor quality of both the grain and the stover. It does indicate 
that soil conditions are more of a factor in corn yield than had been 
recognized, and that proper fertilizing and adequate protection from 
insects can result in higher yields of corn. 

Results of tillage and rotation experiments with corn are given in 
detail in table 30, appendix. 

OATS AND BARLEY 

Oats were not tested adequately in the rotation experiments, partly 
because it was believed that their responses to tillage methods would 
be much the same as those of wheat and partly because their value 
for pasture could not be measured iu these experiments. Five plots 
of spring oats were grown in the two fields. 

Yield of oats (table 10) was higher on wheat land that had been 
fall-plowed than on wheat land that had been disked. It was higher 
on disked cotton land than on disked wheat or fall-plowed alfalfa land. 

Barley, like oats, was not represented adequately in the rotation 
experiments, for the same reasons. Only 2 plots of spring barley and 
1 of winter barley were grown. The only cultural comparison that 
could be made was that between disked cowpeas and disked wheat as 
preparation for barley. Any difference due to sequence was obscured 
by differential damage by insects. 

Table 10. — Yields of spring oats grown in different sequences by 
different tillage methods at Lawton, Okla., 1921^-1+9 



Field, and preceding crop 


Average acre yield, by tillage 
method 


Fall or winter 
plowed 


Disked 


Field A: 

Alfalfa.: 

Cotton 


Bushels 

28. 1 
30. 2 

28. 7 


Bushels 


Field B: 
Wheat 


26. 6 


Cotton 


30. 7 









ALFALFA AND SWEETCLOVER 

For alfalfa and sweetclover, sequence variables were not adequate to 
permit many comparisons. It was evident, however, that yields of 
oats and cotton, the crops immediately following these legumes in 



30 CIRCULAR 951, U. S. DEPARTMENT OF AGRICULTURE 

rotations, were not benefited by them. The stover or hay yields of 
crops that followed the legumes but did not follow them directly 
appear to have been increased slightly by their residual effects. 

DATE-OF- SEEDING AND VARIETY TESTS OF 
WINTER BARLEY 

Date-of-seeding tests with winter barley were carried on for a 
period of 10 years. Seedings were scheduled for 10-day intervals 
from September 15 to November 15. The data do not permit an 
exact comparison of the different specified seeding dates, because in 
each of the 10 years the vagaries of weather and soil conditions pre- 
vented seeding at 1 or 2 of those dates. In order to make a rough 
comparison, the yield figures for all the dates in a year when seedings 
were made were averaged and the average was ascribed to the date 
or dates when seedings could not be made. By this method of cal- 
culation, the following 10-year averages of yield were obtained: 

Acre yield 
Seeding date Bushels 

September 15 19. 4 

September 25 19. 5 

October 5 .' 19. 3 

October 15 18. 

October 25 17. 8 

November 1 .. 17.3 

November 15 15. 6 

Yield in relation to planting date varied widely among individual 
years. Late seeding gave much poorer yields than early seeding in a 
few years, but gave better yields in some. Over the 10-year period, 
yields obtained by seeding on different dates of the period September 
15-October 5 averaged about the same. 

Greater amounts of fall forage were produced by early seedings. 
Apparently the greatest value of the crop can be obtained by planting 
before the middle of October. 

Variety tests of winter barley were made at Lawton during the 
24-year period 1925-48. The results (table 11) ndicate that some of 
the newer varieties have capacities for yield materially above that of 
the check variety, Wisconsin 519. 

The acreage of winter barley in Oklahoma declined greatly during 
the period 1939-47, mainly because of winterkilling and insect pests 
such as greeribugs and chinch bugs. Certain new varieties that 
combine good cold resistance with good yielding ability promise to 
reduce losses from winterkilling. Improved insecticides, and varieties 
that have some natural resistance to greenbugs, give rise to the hope 
that insect damage, also, can be greatly reduced. The unquestioned 
value of winter barley for fall grazing, winter cover, and feed makes it 
an attractive and desirable crop for many farmers in southwestern 
Oklahoma. 



CROP ROTATION, TILLAGE , AND FERTILITY EXPERIMENTS 31 



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32 



CIRCULAR 951. U. S. DEPARTMENT OF AGRICULTURE 



COMPARISON OF FALL-SOWN AND SPRING-SOWN OATS 

Hardy varieties of winter oats, which have come into prominence 
in recent years, were grown on the Lawton station in 5-year variety 
tests (27) in which they were compared with spring-sown varieties. 

Yield of spring oats in this 5 -year test (table 12) averaged about the 
same as in the rotations over the 26-year period. The proportion of 
loss of the spring oats crop, 2 crops in 5, was somewhat greater than 
in the rotation tests. Invariably, the fall-sown oats produced much 
greater yields than the spring-sown oats. 

In farming systems for southwestern Oklahoma that include live- 
stock production, fall-sown oats can be used to great advantage for 
both pasture and grain. 

Table 12. — Grain yields of fall -sown and spring-sown oats in a 5 -year 
comparative test at Lawton, Okla., 1943-4-7 



Time of seeding 


Annual acre yields l 


1943 


1944 


1945 


1946 


1947 


Average 


Fall 

Spring 


Bushels 
35. 4 

( 2 ) 


Bushels 
79. 

44. 8 


Bushels 
88. 9 
37. 


Bushels 
85. 9 

( 3 ) 


Bushels 
87. 8 
51.4 


Bushels 
75. 4 
28. 6 



1 Values are averages for the 3 highest yielding varieties. 

2 Crop destroyed by spring freeze. 

3 Crop destroyed by greenbugs. 

NITROGEN CONTENT OF CROPPED SOIL 

Soil samples from plots that had been subjected to different cropping 
treatments were collected and analyzed in 1947. Since samples had 
not been taken on the plots when the experimental work was started, 
the only available measure of the extent of change was comparison 
with the virgin soil of a nearby area. The results of such comparison, 
combined by treatment groups, are presented in table 13. 

Reduction of nitrogen content of the 0-to-6-inch layer of soil, as 
measured, was tremendous, ranging from 42 to 62 percent. Even 
under continuous small grain, usually one of the cropping practices 
least exhaustive of soil nitrogen, the indicated losses averaged about 
45 percent. Under continuous row crops, or row crops alternating 
with fallow, they averaged about 60 percent. 

Manure, which was very effective in increasing yields of most crops, 
was not effective in maintaining the nitrogen content of the soil. 
(Some evidence is presented in the following section, however, that it 
helped maintain the phosphorus content.) 

Plowing under a crop of cowpeas every other year did not reduce 
the loss of nitrogen in the 0-to-6-inch layer of soil measurably below 
that incurred when the cowpeas were removed as hay. 

Losses of nitrogen took place in the 6-to-12-inch layer of soil, but 
they were much smaller than those in the surface layer. Although 
the virgin soil contained about 50 percent more nitrogen in the surface 



CROP ROTATION, TILLAGE, AND FERTILITY EXPERIMENTS 33 

Table 13. — Nitrogen content of cropped soil at the Lawton Field Station in 1947 
and its percentage change in 25 to 32 years under various cropping methods 



Cropping method 



Continuous small grains, plowed or basin listed. 
Continuous small grains, alternately plowed 

and disked 

Continuous small grains, disked 

Continuous small grains, basin listed, manured. 

Alternate small grains and fallow 

Alternate small grains and fallow, manured 

Continuous row crops 

Alternate row crop and fallow . 

Alternate row crop and fallow, manured 

Alternate small grain and row crop 

Alternate small grain and cowpeas 

Alternate small grain and cowpeas (plowed 

under) 

Alternate small grain (topdressed) and cowpeas. 
Virgin sod 



Year 
started 



1923 2 

1923 

1923 

1923 

1919 

1919 

1916 

1916 2 

1919 

1923 

1919 

1919 
1919 



Plots 



Number 



Average nitrogen content at depth 
of— 



to 6 inches 



1947 Change > 



Percent, 
0.082 

.082 
.088 
.081 
.078 
.085 
.058 
.061 
.064 
.081 



.082 
.090 
.154 



Percent 

-47** 

-47** 
-43** 
-47** 
-49** 
-45** 
-62** 
-60** 
-58** 
-47** 



-47* 
-42* 



6 to 12 inches 



1947 Change 



Percent 
0.085 



0S4 
078 
080 
079 
081 
075 
084 
091 



094 
10:5 



Percent 
-17** 

-1.** 
-1. 

-18* 

-24* 

-22* 

-23** 

-21** 

-27** 

-18* 

-12 

-16 



1 1 asterisk indicates significance at the 5-percent level. 2 asterisks indicate significance at the 1-percent 
level. Changes were calculated on the basis of the nitrogen content, in 1947, of the virgin soil of a nearby 
area. No significant differences were found between changes at the 6-tc-12-inch depth associated with 
different cropping methods. Least significant differences between changes at the 0-to-6-inch depth asso- 
ciated with any two cropping methods are as follows: 



Level of signifi- 


L. S. D., by numbers of plots subjected to the two treatments being compared 


cance (percent) 


1 v. 4 


1 v.2 


lv. 4 


lv. 5 


lv. 6 


2 v.2 


2v. 4 


2v. 5 


2v. 6 


4v. 4 


4v. 5 


4v. 6 


5v. 6 


5 : 

1 


Pet 
14 
19 


Pet. 
12 
16 


Pet. 

11 
15 


Pet. 
11 
15 


Pet. 
10 
14 


Pet. 
10 
14 


Pet. 
8 
12 


Pet. 
8 
11 


Pet. 
8 
11 


Pet. 
7 
10 


Pet. 
6 
9 


Pet. 
6 
9 


Pet. 
6 
8 







2 For 1 plot, 1919. 



layer than in the 6-to-l 2-inch layer, by 1947 the cropped soil contained 
slightly less nitrogen in the surface layer than in the 6-to-l 2-inch layer. 

Measurements of carbon content of the soil were made for some 
but not all of the plots. Carbon-nitrogen ratio was found not to vary 
significantly with cropping treatment; therefore nitrogen changes can 
be used as a reliable measure of relative changes in the organic carbon 
content of the soil. The soil's carbon-nitrogen ratio was slightly lower 
on cropped land than on virgin land. 

The results of the analyses, fragmentary as they are, certainly 
demonstrate that there is no easy way to maintain the nitrogen and 
organic carbon of soils under conditions such as those at Lawton. 
Building up the organic-matter content of the soil by any practicable 
means appears to be difficult if not impossible. 

The physical condition of the soil seemed to have changed for the 
worse during the time that the area had been under cultivation. 
This was evidenced by increased difficulty in performing cultural 
operations and by increased runoff during torrential summer rains. 
Grasses and legumes have been suggested as means of building up 
the soil, but it seems highly probable that their chief benefit is in 



34 



CIRCULAR 951, U. S. DEPARTMENT OF AGRICULTURE 



bettering its physical condition and in preventing further soil and 
fertility losses during the time that they occupy the land. 

TESTS WITH COMMERCIAL FERTILIZERS 

The heavy losses in nitrogen and carbon revealed by the 1947 
analyses made it appear likely that the soil had reached such a con- 
dition that fertility rather than moisture was limiting crop yields. 
The generally good results from manure, and spectacular increases in 
grass-seed yields associated with nitrogen applications in a 1946-47 
experiment, made it appear likely that nitrogen was the chief limit- 
ing factor. Experiments were conducted in 1948 and 1949 to deter- 
mine the responses of major field crops to fertilizer. These were too 
brief to furnish any reliable measure of the average increases that 
might be attained through fertilizers, but they did furnish some 
important information. 

SEED YIELDS OF WEEPING LOVEGRASS 

Nitrogen in the form of ammonium nitrate was applied at different 
rates in 1946 and 1947 to a stand of weeping lovegrass {Eragrostis 
curvula) established in 1944. As little as 30 pounds of nitrogen to 
the acre produced spectacular increases in seed yields, averaging 119 
pounds to the acre in 1946 and 301 pounds to the acre in 1947 (fig. 11). 



NITROGEN ADDED PER ACRE 



1946 



1947 



NONE 



165 



80 



30 POUNDS 
60 POUNDS 
90 POUNDS 
120 POUNDS 
180 POUNDS 



■■- .j 284 nm 


;,,:?>f-.^B38l 


V |264 


i ; --iC ' ^421 


(321 /. ||| 


J 410 


■ 310 


■ 396 


1324 
1 — 1 it 


^■446 
1 . 1 1 



200 400 200 400 

ACRE YIELDS OF SEED (POUNDS) 



600 



Figure 11. — Seed, yields of weeping lovegrass on soil variously treated with 
nitrogen at Lawton, Okla. 

Additional quantities of nitrogen produced only small further increases 
in yield. 

Hay yields of weeping lovegrass were not determined, but a material 
increase in vegetative growth was observed where nitrogen had been 
applied. It was further observed that work mules ate the hay from 
the fertilized land readily although they refused that from the un- 
fertilized land. 



CROP ROTATION, TILLAGE, AND FERTILITY EXPERIMENTS 35 

SORGHUM 

An experiment on kafir was conducted in 1948 to determine (1) what 
effect application of nitrogen had on kafir grain and fodder yields and 
(2) whether delayed application of nitrogen would benefit the crop 
without producing the stimulation of early growth that had often 
resulted in severe firing of manured plots. " A few phosphorus treat- 
ments were included to obtain evidence on whether phosphorus might 
be deficient. 

The experiment was conducted on land that had been in kafir for 
more than 30 years and had probably lost at least 60 percent of its 
original nitrogen. The results (table 14) were as positive as they were 
surprising. No benefit whatever resulted from applying nitrogen, 
regardless of quantity or time of application; the plots receiving nitro- 
gen alone were not observably different from the checks. On all the 
plots receiving phosphorus, the kafir produced materially greater 
yields and ripened at least a week earlier than on the check plots. 
Nitrogen in addition to phosphorus did not increase yields signifi- 
cantly. 

This experiment made it appear that, at least as far as sorghums 
were concerned, response to manure was chiefly a response to its 
phosphorus rather than to its nitrogen content. This was confirmed 
by a single replication of the experiment on land that had been in 
manured kafir for more than 30 years. On this manured land, kafir 
showed no response to application of either nitrogen or phosphorus. 

In 1949 a test was made of the effects of applications of phosphorus 
with and without nitrogen on kafirita. Phosphorus was applied at the 
per-acre rates of 25, 50, and 100 pounds of P2O5, and nitrogen at that 
of 30 pounds. There was one delayed application of nitrogen. At 
no time during the season was there an observable difference between 

Table 14.- — Yields of kafir on soil variously treated with commercial 
fertilizers at Lawton, Okla., 1948 



Fertilizer applied per acre and time of application 



Acre yields 



Grain Stover 



No fertilizer 

30 pounds N: 

At seeding 

4 weeks after seeding 

6 weeks after seeding 

8 weeks after seeding 

60 pounds N, 6 weeks after seeding 

100 pounds P 2 5 , at seeding 

100 pounds P 2 5 and 30 pounds N, at seeding 

100 pounds P 2 5 , at seeding; 60 pounds N, 6 weekt 
after seeding 

L. S. D. at 5-percent level 



Bushels 
14. 



14. 2 
8. 8 
14.7 
11. 2 
11. 8 

19. 6 

20. 6 

20. 5 



Pounds 
4,000 

3,940 
3, 100 
3,980 
3, 930 

3, 540 
4,970 

4, 540 

4, 560 



3. 8 



490 



36 



CIRCULAR 951, U. S. DEPARTMENT OF AGRICULTURE 



the plots to which nitrogen had been applied and the other plots.. 
Early growth and vigor of the crop varied in direct proportion to the 
quantity of phosphorus applied. On plots receiving P 2 5 at the 25- 
pound rate kafir showed only slightly greater early vigor; on those re- 
ceiving it at the 50-pound rate kafir was markedly more vigorous ; and 
on those receiving it at the 100-pound rate, kafir showed outstanding- 
vigor comparable to that on the manured plots. For a tim.e the plots 
that had received the 100-pound P 2 5 treatment appeared to be 
capable of producing yields more than double those on plots that had 
received little or no phosphorus. Protracted drought during July 
and August checked the vegetative growth on all plots and reduced 
grain yields to near failures. The vigorous kafir that had made the 
most growth suffered first. The final yields did not differ significantly 
according to treatment, either in weight of grain or in total weight... 
This experiment demonstrated that the soil was seriously deficient in 
phosphorus, and also demonstrated that fertility differences did not 
result in yield differences when moisture was deficient. 

Within the period of operation of the Lawton Field Station, appar- 
ently, the proportion of phosphorus in the soil of plots cropped con- 
tinuously to sorghums dropped from an original average of about 260 
parts per million to about 180. 5 This reduction, which is greater than 
that in soil cropped to small grains or in soil cropped to small grains 
and row crops in rotations, is evidently enough to make phosphorus a 
limiting factor in sorghum production. Row-crop land that was 
manured each year continued to contain about 210 parts per million 
of phosphorus. 

WHEAT AND OATS 

Tests of the effects of nitrogen and phosphorus treatments on yields 
of winter wheat aud winter oats were conducted during the 1948-49 
crop season, on soil in a somewhat better fertility condition than that 
on which the sorghum tests were made. The experiment involved 
both quantity of nitrogen applied and time of application. Yields ob- 
tained where nitrogen alone was applied differed little or not at all 
from those of the check plots (table 15). Application of phosphorus 



Table 


15.— Yit 


Ids of winter wheat and winter oats on soil variously treated with 
commercial fertilizers at Lawton, Okla., 1949 


Fertilizer application per acre 


Acre yields 


Fertilizer application per acre 


Acre yields 


P2O5, fall 


Nitrogen 


Winter 
wheat 


Winter 
oats 


P2O5, fall 

(pounds) 


Nitrogen 


Winter 
wheat 


Winter 


(pounds) 


Fall 


Spring 


Fall 


Spring 


oats 





Pounds 

f ° 

20 

1 
W o 

[ 20 


Pounds 



20 


10 



Bushels 
13.9 
12.7 
12.0 
16.1 
17.9 
16.5 


Bushels 
54.1 
52.2 
50.8 
60.6 
60.1 
56.1 


30 


Pounds 

f 

10 
40 


10 




Pounds 
20 
10 


40 
30 




Bushels 
17.3 
19.9 
15.4 
17.0 
17.1 
17.9 

1.2 


Bushels 
63.9 
59.4 


30 


56.8 
60.3 
63.3 
61.3 


L.S. D.at5-nercentl 








2.3 















5 Unpublished data from analyses made at the Northern Great Plains Field 
Station, Mandan, N. Dak. 



CROP ROTATION, TILLAGE, AND FERTILITY EXPERIMENTS 37 

alone increased yields as much as did applications of both nitrogen and 
phosphorus. The quantity or time of application of nitrogen made 
little difference; spring or split applications tended to give slightly 
better results than fall applications. 

COTTON 

A preliminary experiment with cotton was conducted in 1949. This 
involved the same phosphorus applications as the kanrita experiment 
and a single nitrogen treatment. The cotton did not show any ob- 
servable difference in early growth or vigor according to quantity of 
phosphorus applied. Neither did it show any effect, beneficial or 
otherwise, from nitrogen. All yields were greatly reduced by drought 
in July and August. Yield did not vary significantly according to 
treatment, although it was slightly better where the fertilizer treat- 
ments had been applied. 

RESULTS WITH GRAPES, TREES, SHRUBS, AND GRASSES 

GRAPES 

A small vineyard consisting of a few vines each of about 20 varieties 
was planted in 1923. A few other varieties were added later. 

The Lawton silt loam soil is not well adapted to grapes, most vari- 
eties of which prefer a deep, fertile sandy or sandy loam soil. Vine 
growth was restricted, and in dry seasons the fruit of some of the 
varieties shriveled instead of ripening properly and was worthless. 
Commercial growing of grapes should not be attempted on soil of this 
type, but a few selected varieties can well be grown on it for home use. 

In spite of the unsuit ability of the soil, 10 varieties made average 
annual yields of 10 to more than 14 pounds per vine over a period of 
years. Some of the varieties suffered drought damage in the dry 
years, and some of these and others suffered from black rot in wet 
years. Grapes of some of the higher yielding varieties are poor in 
quality and satisfactory only for juice and jellies. The vineyard was 
heavily damaged by June bugs. A small vineyard often suffers very 
severe damage from birds and from insects, particularly wasps. 
Black rot and some of the insects can be controlled by proper spraying. 

Extra is the only one of the varieties tested that can be generally 
recommended for home use on Lawton silt loam. Delaware made 
rather low yields, but a few vines of this variety might be included 
to extend the season with a high-quality table grape. A few vines of 
American, with Beacon as a pollinator, might also be included for 
juice and jellies. Cleota produced dependably, and its grapes were 
satisfactory for table use when fully vine ripened. (It is doubtful, 
however, that vines of this variety are now available commercially.) 

Many grape varieties that did not do well in the station vineyard 
make creditable yields on the sandy soils of southwestern Oklahoma. 
On these soils, the Oklahoma Agricultural Experiment Station (2) 
has advised, 

Extra should be the leading commercial variety, with Carman and Bailey 
grown on a small scale for trial as grapes that may develop into commercial 
varieties, and Beacon, America, Niagara, Ellen Scott, Armalage, Catawba 
and Last Rose grown to give a wide variety for home use and local market. 



38 



CIRCULAR 95 1 ; U. S. DEPARTMENT OF AGRICULTURE 



TREES AND ORNAMENTAL SHRUBS 

Deciduous trees, evergreens, and hardy flowering shrubs may well 
be used in southwestern Oklahoma to provide beauty, comfort, and 
protection for the farm homestead. Appropriate plantings add much 
to the appearance and value of the farm and help in keeping farm 
boys and girls on the land. 

Many trees and shrubs grown on the Lawton Field Station proved 
hardy and useful on ground of medium fertility, under wide variations 
of rainfall and in spite of droughts and destructive storms. Among 
the trees tested, Arizona cypress (Cupressus arizonica) thrived par- 
ticularly well (fig. 12). Many ornamental shrubs not included in 
the station tests may be well adapted to the area (17). 

The following tree and shrub species and varieties are recommended 
for planting in southwestern Oklahoma, almost entirely on the basis' 
of their behavior in station plantings: 

Deciduous trees: 

American elm (Ulmus americana) 

Apricot (Prunus armeniaca) 

Black walnut (Juglans nigra) 

Common hackberry (Celtis sp.) 

Common jujube or Chinese date (Zizyphus jujuba) 

Double red peach (Prunus persica) 

Green ash (Fraxinus pennsylvanica lanceolata) 

Small-leaved elm (Ulmus parvifolia) 

Sycamore (Platanus occidentalis) 

Thornless honevlocust (Gleditsia triacanthos inermis) 




Figure 12. — Arizona cypress growing at the Lawton Field Station. 



CROP ROTATION, TILLAGE, AND FERTILITY EXPERIMENTS 39 

Evergreen trees: 

Arizona cypress {Cupressus arizonica) 

Cherrystone juniper {Juniper us monosperma) 

Colorado juniper {Juniperus scopulorum) 

Pfitzer juniper {Juniperus chinensis pfitzeriana) 

Redcedar {Juniperus virginiana) 

Savm juniper {Juniperus sabina) 

Silver juniper {Juniperus virginiana glauca) 
Flowering shrubs and ornamentals: 

Amur privet {Ligustrum amurense) 

Anthony Waterer spirea {Spiraea bumalda) 

Crapemyrtle {Lager sir oemia indica) 

Desertwillow {Chilopsis linearis) 

Douglas spirea {Spiraea douglasii) 

Eyerblooming honeysuckle {Lonicera heckrottii) 

Firethorn {Pyracantha coccinea lalandii) 

Flame-leaf sumac {Rhus copallina) 

Flowering quince {Chaenomeles lagenaria) 

Glossy abelia {Abelia grandiflora) 

Kashgar tamarix {Tamarix hispida) 

Mockorange {Philadelphus virginalis) 

Xandina {Nandina domestica) 

Rose-of-Sharon or shrub-althea {Hibiscus syriacus) 

Thunberg spirea {Spiraea thunbergii) 

Trumpet honeysuckle {Lonicera sempervirens) 

Vanhoutte spirea {Spiraea vanhouttei) 

Vitex {Vitex angus-castus) 

Weeping quihoui privet {Ligustrum quihoui pendulum) 

Planting plans must be adapted to and developed for individual 
farm homes. They will vary in accordance with topography, soil, 
and the number and kind of farm structures. 

Careful planting when the soil is well filled with water, and later 
cultivation, are essential to the establishment of good root systems 
that will promote vigorous growth the first year. After the first 
year the chief requirements are continued elimination of competing 
weeds, careful pruning, and control of the few diseases and insect 
pests that are prevalent in the area. 

GRASSES 

No extensive grass experiments were carried out at the station, but 
because of the need for a soil-binding crop a few simple exploratory 
tests were made on the establishment of stands of important native 
grasses and recently introduced foreign grasses. Such tests were 
made both on the station and on a number of farms representing 
average farm conditions in Comanche County and several adjoining 
counties of southwestern Oklahoma. 

Weeping lovegrass was seeded in 1944 on the station and on farms 
in Comanche County, on clean cultivated land. The station plantings 
consisted of two 1-acre blocks and a number of small plots, which 
were seeded at intervals from April 5 to September 15. Good stands 
resulted from all these seedings. In the first year the grass made 
good vegetative growth but produced practically no seed. Vigorous 
growth and satisfactory seed yields were obtained in 1945, the second 
year. Seed yields in 1946 and 1947 were stimulated by nitrogen 
fertilizer, as discussed earlier. 

The farm seedings of weeping lovegrass consisted of 1- to 1%-acre 
blocks on 5 farms. All these seedings were made in the spring. Only 
one of them resulted in a satisfactory stand. 



40 



CIRCULAR 951, U. S. DEPARTMENT OF AGRICULTURE 



Sand lovegrass (Eragrostis trichodes) was seeded on the station in 
1945 and 1946 in rows at 7-inch and 22-inch intervals. Good stands 
were obtained each year in both spacings, but negligible vegetative 
growth and seed production in succeeding years demonstrated 
emphatically that this grass is not adapted to heavy soils. 

Buffalo grass sprigs were planted in 1946, spaced 2 feet apart in 
rows 40 inches apart. The grass demonstrated its high adaptation 
by completely covering the ground surface the first year. 

Sowing of side-oats grama seed in 40-inch rows resulted in good 
stands. The grass grew vigorously and gave evidence of seed pro- 
duction good enough to justify harvesting for the purpose of increasing 
the supply of seed of desirable strains. 

Failures to obtain stands of grasses through seeding on farms are 
believed to be due more often to covering the seed too deeply than to 
any other single cause. This belief led to construction of a grass- 
seeding drill (fig. 13). Cooperation in this project was received from' 
the Lawton Chamber of Commerce and from H. C. Hyer, Extension 
Division, Oklahoma Agricultural and Mechanical College. 

Seedings of a grass mixture were made on farms selected as repre- 
sentative of southwestern Oklahoma's soil types and topography. 
The mixture consisted of little bluestem, blue grama, side-oats grama, 
and buffalo grass. On the whole, the seedings were successful. 
Subsequent additional seedings made under soil conservation district 
direction now cover several thousand acres. Most of the seedings 
were on land that does not produce row crops or small grains profit- 




Figure 13. — Grass-seeding drill constructed at the Lawton station. This drill 
permits planting nearly all types of grass seed at a controlled uniform shallow 
depth and packs the soil firmly over the seed. 



CROP ROTATION, TILLAGE, AND FERTILITY EXPERIMENTS 41 

ably. It seems evident that the fertilizer needs of such areas must 
T)e determined and met before the areas are regrassed, if production 
potentialities are to be realized. 

CROPPING SYSTEMS ADAPTED TO THE AREA 

Out of the combination of practical farming experience and the 
xesults of research, certain principles have evolved that point the way 
to a profitable permanent agriculture for southwestern Oklahoma. 

In mixed farming on the uplands of southwestern Oklahoma, the 
surest system for a regular cash income is raising livestock on home- 
grown feed. The first essential of such a system is to produce feed 
sufficient to support the maximum number of livestock through good 
years and bad. Crops with which this requirement can be fulfilled 
are grain and forage sorghums for roughages, winter oats for grazing 
and feed, and winter wheat and cotton for cash crops and for protein 
supplements. In addition, either native or reseeded grassland must 
be available for grazing. Legume crops such as cowpeas, Mung beans, 
and (on sandy soils) hairy vetch are good producers of hay rich in 
protein; but when harvested for hay they do nothing to improve or 
maintain soil productivity. Sweetclover grown in paired cultivated 
rows affords considerable grazing in late fall and early spring, produces 
a, profitable yield of seed the second year, and is one of the best 
available means of maintaining soil productivity. 

A cropping system for upland mixed farming must be extremely 
flexible and must be governed by current weather conditions. Dry 
weather, wet weather, or destructive storms will modify cropping 
plans but will not necessarily defeat them. The farmer has the 
option of using substitute crops when weather conditions are adverse 
to the ones he has planned to grow. 

Crops are at the mercy of the elements from planting time until 
harvest. Variations in temperature, sunshine, and rainfall cause large 
variations in yield from year to year. Weather hazards are reduced 
by timely tillage, moisture conservation, and prevention of weed 
growth and of abnormal soil erosion. 

A simple 4-year rotation that produced reasonably good yields 
consistently for more than 30 years at the Lawton station consists of 
oats, kafir, cowpeas, and cotton, with barnyard manure applied to 
the kafir. This rotation provides some pasture, kafir grain and 
forage, a legume hay, and a cash crop. Such a rotation is susceptible 
of changes that may better fit it to the individual operator's farm 
needs. For example, wheat may be substituted for oats, a combine 
sorghum or sorgo for kafir, and some other legume and other cash 
crop for cowpeas and cotton. Application of barnyard manure to 
one-fourth of the cropped land each year as in this rotation is im- 
practicable unless much feed is bought, but the results of limited 
fertilizer experiments indicate that much of the benefit obtainable 
from manure can be obtained through use of commercial fertilizers. 
These should supplement available manure rather than replace 
manure. 

The crops in the rotation discussed are suitable also for sandy soils; 
but on such soils a rotation including sweetclover, hairy vetch, and 
early maturing corn is likely to give better results. 



42 CIRCULAR 951, U. S. DEPARTMENT OF AGRICULTURE 

On creek and river bottom lands alfalfa becomes the backbone of 
the farming system. An operator who controls several hundred acres 
of land of this type generally has a large investment in livestock. 
On land not in alfalfa, his cropping is directed toward producing 
wheat and oats, for grazing in all years and for grain in the more 
productive years, and toward maintaining the productivity of 
grasslands. 

A farming system, to be profitable and maintain productivity, must 
hold soil losses to the minimum, prevent unnecessary water loss 
through runoff, prevent weed growth, make use of the most suitable 
crop varieties and cropping practices, and use all practicable means 
of maintaining soil fertility. In most cases profitable farming in- 
volves using suitable quantities of needed commercial fertilizers to 
improve yields and help maintain soil fertility. 

Reserves of livestock feed must be created in favorable years, for 
failures or low yields must be expected in about 1 year out of 4. Such • 
reserves become especially valuable in a succession of low-production 
years. 

A stable s} T stem of farming in southwestern Oklahoma requires a 
diversity of crops, livestock such as beef or dairy cattle or both, 
timely preparation of seedbeds, use of the best crop varieties, and 
space in which to store surplus feeds. 

The weather at Lawton during the years 1916-49 was representative 
of that during the 75 years for which local weather records are avail- 
able. Yields obtained during this period are indicative of those that 
might be obtained over a longer period. 

SUMMARY AND CONCLUSION 

The Lawton Field Station was established at Lawton, Okla., in 
1915, for the purpose of determining possibilities and limitations of 
crop production in southwestern Oklahoma. Supplemental work 
consisted in variety tests of the principal cultivated crops, studies in 
crop adaptation, biological studies of insects, and crop-plant breeding 
for disease and insect resistance. The station's activities continued 
through 1949. 

Annual precipitation on the station area within the 34-year period 
1916-49 ranged from 17.23 to 43.92 inches. Monthly precipitation 
ranged from to 14.12 inches. Rainfall distribution, rather than 
annual or monthly totals of rainfall, is a critical factor in crop produc- 
tion in southwestern Oklahoma. 

Temperatures ranged from a maximum of 115° F. to a minimum of 
— 9°. Maximum temperatures for the summer months were regularly 
high. The annual frost-free period averaged 214 days. 

Injurious crop insects and plant diseases were a constant threat, 
necessitating quick and effective control measures. 

The soil of the station area is Lawton silt loam. Its slow perme- 
ability and the torrential character of summer and fall rains made 
runoff and soil erosion a serious problem. 

Losses of nitrogen from the 0-to-6-inch layer of the soil while the 
land was under cultivation ranged from about 45 percent under 
continuous cropping to small grain to about 60 percent under continu- 
ous row cropping. Applications of stable manure were not effective 



CROP ROTATION, TILLAGE, AND FERTILITY EXPERIMENTS 43 

in reducing losses of nitrogen, and plowing cowpeas under did not 
reduce the losses. 

Tillage experiments with row crops and small grains indicated that 
timeliness of operations is very important. Early tillage that de- 
stroyed weeds and left the land receptive to rainfall was much more 
productive than tillage beginning shortly before seeding or planting. 

Plowing to a depth of about 8 inches gave better results than shal- 
low tillage. Little evidence was found that any crop other than corn 
was benefited by loosening the soil to a depth of 18 or 20 inches rather 
than 8 inches. 

Listing for small grains was not so productive as plowing. Listing 
as a substitute for plowing produced higher yields of corn, but pro- 
duced much lower yields of other row crops than plowing. 

The expensive practice of plowing under crops of cowpeas or rye 
increased yields somewhat, but not enough to compensate the loss of 
a, harvest. 

Yields of both row crops and small grams were increased by summer 
fallowing, but not enough to justify the practice. Fallowing as a 
preparation for growing wheat is justified under certain special 
conditions. 

Manure increased the grain yield or the vegetative growth, or both, 
of all crops and appeared to give cumulative benefit to rotations in 
which it was applied. It was particularly effective on corn grain and 
stover and on sorghum stover. The quantities needed for sustained 
crop production, however, are not produced in the course of general 
farming operations. 

In preliminary commercial-fertilizer experiments, sorghums re- 
sponded strongly to phosphorus but not to nitrogen. Weeping love- 
grass responded to nitrogen with spectacular increases of seed, ma- 
terial increase of forage, and improved palatability of forage removed 
as hay. Application of nitrogen did not materially increase the 
yield of winter wheat or that of fall-sown oats, but application of 
phosphorus increased both to some extent. In a 1-year test, cotton 
showed no benefit from application of either phosphorus or nitrogen. 

A relatively stable mixed-farming system for southwestern Okla- 
homa can be attained by making productive use of existing informa- 
tion. Farming systems best adapted to the area appear to be those 
in which production of livestock and of feed for livestock is the main 
enterprise. Cash crops are highly desirable. Rotations that produce 
pasture and feed for livestock plus a cash crop are well adapted to the 
tight soils of the upland. Sorghums, cowpeas, and corn are grown 
primarily for feed. Winter oats, winter barley, and sweetclover are 
combined pasture and feed or seed crops. Wheat and cotton are the 
principal cash crops. 

A well-balanced farming system provides for applying the man me 
produced on the farm to the crop that responds most strongly to it. 
Additional benefits may be obtained by supplementing the manure 
with commercial fertilizers. Choice of fertilizer treatment must be 
governed by (1) the nature of soil deficiencies, (2) the crops to be 
grown, and (3) the probability that prospective resulting increases in 
yields can be maintained in the face of frequent critical moisture 
deficiencies. Most of the details of when and how to use fertilizers 
in southwestern Oklahoma remain to be worked out. 



44 CIRCULAR 95 1. U. S. DEPARTMENT OF AGRICULTURE 

Field management is important. If both small grains and corn or 
sorghum are grown, the fields must be well separated to protect the 
corn or sorghum from chinch bugs. 

Successful farming also requires selection of crop varieties best 
adapted to the section and storing of feed, reserves from years of high 
production. 

LITERATURE CITED 

(1) Atkins, I. M.. and Dahms. R. G. 

1945. REACTION OF SMALL- GRAIN VARIETIES TO GREEN BUG ATTACK. U. S. 

Dept. Agr. Tech. Bui. 901. 30 pp.. illus. 

(2) Cross, F. B., and Locke. L. F. 

1929. grapes in Oklahoma. Okla. Agr. Expt. Sta. Cir. 254. 35 pp.. 
illus. 

(3) Dahms. E. G. 

1937. NUMBER OF SHORT-WINGED CHINCH BUGS PRODUCED UNDER LABORA- 
TORY conditions. Jour. Econ. Ent. 30: 803-804. 

(4) 

1943. insect resistance in sorghums and cotton. Amer. Soc. Agron. 
Jour. 35: 704-715. 
(5) 

(7) 



1945. rice stinkbtjg as a pest of sorghums. Jour. Econ. Ent. 35: 
945-946. 



194 < . ovipo.-ition and longevity of chinch bugs on seedlings grow- 
ing in nutrient solutions. Jour. Econ. Ent. 40: 841-845. 



1948. EFFECT OF DIFFERENT VARIETIES AND AGES OF SORGHUM ON THE 

biology of the chinch bug. Jour. Agr. Res. 76: 271-288, illus. 

(8) and Fenton. F. A. 

1939. PLANT BREEDING AND SELECTING FOR INSECT RESISTANCE. Jour. 

Econ. Ent. 32: 131-134. 

(9) and Fenton. F. A. 

1940. THE EFFECT OF FERTILIZERS ON CLINCH BUG RESISTANCE IN SOR- 
GHUMS. Jour. Econ. Ent. 33: 688-692, illus. 

10 and Fenton, F. A. 

1942. EXPERIMENTS WITH POISONED BAIT TO CONTROL ARMYWORMS IN 

wheat. Jour. Econ. Ent. 35: 439-440. 
;11' and Kagan. M. 

1939. egg predator of the chinch bug. Jour. Econ. Ent. 31: 779-780. 
(12) and Martin, J. H. 

1940. RESISTANCE OF Fj SORGHUM HYBRIDS TO THE CHINCH BUG. Amer. 

Soc. Agron. Jour. 32: 141-147. illus. 
1 13- and Osborn, W. M. 

1942. EFFECT OF CERTAIN WEATHER CONDITIONS ON CHINCH BUG ABUN- 
DANCE AT THE DRY LAND FIELD STATION OF THE UNITED STATES 
DEPARTMENT OF AGRICULTURE AT LAWTON. OKLA., 1916-40. EcoloaT 

23: 103-106. 

(14) Snelling. R. O.. and Fenton. F. A. 

1936. EFFECT OF DIFFERENT VARIETIES OF SORGHUM ON BIOLOGY OF THE 

chinch bug. Amer. Soc. Agron. Jour. 28: 160-161. 

(15) — Snelling. R. O.. and Fenton. F. A. 

1936. EFFECT OF SEVERAL VARIETIES OF SORGHUM AND OTHER HOST 
PLANTS ON BIOLOGY OF THE CHINCH BUG. JoilT. EcOIl. Ent. 29: 

1147-1153. illus. 

(16) Green, J. M., Keathlev. M: G.. Oswalt, E. S.. and Gober. N. M.. Jr. 

1952. OKLAHOMA COTTON VARIETIES; VARIETAL DESCRIPTIONS. AND 
PERFORMANCE TEST RESULTS. 1945-1951. Okla. Agr. Expt. Sta. 

Bul. B-381. 15 pp., illus. 
(17. Johnson. E. W. 

1951. ORNAMENTAL SHRUBS FOR THE SOUTHERN GREAT PLAINS. U. S. 

Dept. Agr. Farmers' Bul. 2025. 62 pp., illus. 



CROP ROTATION, TILLAGE, AND FERTILITY EXPERIMENTS 45 

(18) Kiltz, B. F., Sieglinger, J. B., Osborn, W. M., and others. 

1933. sorghums for grain and forage. Okla. Agr. Expt. Sta. Bui. 
210, 48 pp., illus. 

(19) Leukel, R. W., Martin, J. H., and Lefebvre, C. L. 

1951. sorghum diseases and their control. U. S. Dept. Agr. Farm- 
ers' Bui. 1959, 50 pp., illus. (Rev.) 

(20) Mariin, J. H., Sieglinger, J. B., Swanson, A. F., and others. 

1929. SPACING AND DATE-OF-SEEDING EXPERIMENTS WITH GRAIN SOR- 
GHUMS. U. S. Dept. Agr. Tech. Bui. 131, 46 pp., illus. 

(21) Osborn, W. M. 

1932. ROTATION AND TILLAGE EXPERIMENTS AT THE LAWTON (OKLA.) 

field station, 1917-30. U. S. Dept. Agr. Tech. Bui. 330, 34 pp., 
illus. 

(22) 



1933. cotton experiments at the lawton (Oklahoma) field station, 
1916-1931. Okla. Agr. Expt. Sta. Bui. 209, 31 pp., illus. 

(23) Painter, R. H., Snelling, R. O., and Brunson, A. M. 

1935. HYBRID VIGOR AND OTHER FACTORS IN RELATION TO CHINCH BUG 

resistance in corn. Jour. Econ. Ent. 28: 1025-1030, illus. 

(24) Parrott, I. M., Gober, N. M., Jr., and Green, J. M. 

1950. cotton varieties for Oklahoma. Okla. Agr. Expt. Sta. Bui. 
B-343, 11 pp. 

(25) Gober, N. M., Jr., and Green, J. M. 

1950. OKLAHOMA COTTON VARIETY TESTS, 1944 TO 1948. Okla. Agr. Expt. 

Sta. Tech. Bui. T-37, 46 pp. 

(26) Schlehuber, A. M., Hubbard, V. C., Osborn, W. M., and others. 

1946. WINTER WHEAT VARIETIES FOR OKLAHOMA. Okla. Agr. Expt. 

Sta. Bui. B-297, 36 pp., illus. 
(27) Osborn, W. M., and Johnston, T. H. 

1948. OAT VARIETY AND CULTURAL TESTS IN OKLAHOMA, 1925-1947. Okla. 

Agr. Expt. Sta. Tech. Bui. T-33, 39 pp., illus. 

(28) Osborn, W. M., and Johnston, T. H. 

1948. better oats for Oklahoma. Okla. Agr. Expt. Sta. Bui. B-322, 
24 pp., illus. 

(29) Snelling, R. O. 

1936. third generation and method of migration of chinch bug 
in southwestern Oklahoma. Jour. Econ. Ent. 29: 797-803, 
illus. 

(30) and Dahms, R. G. 

1937. resistant varieties of sorghums and corn in relation to 
chinch bug control in Oklahoma. Okla. Agr. Expt. Sta. Bui. 
232, 22 pp., illus. 

(31) Painter, R. H., Parker, J. H., and Osborn, W. M. 

1937. resistance of sorghums to the chinch bug. U. S. Dept. Agr. 
Tech. Bui. 585, 56 pp., illus. 

(32) Webster, J. E., and Heller, V. G. 

1942. THE CHEMICAL COMPOSITION OF ATLAS AND DWARF YELLOW MILO 
PLANTS IN RELATION TO CHINCH BUG RESISTANCE. Okla. Agr. 

Expt. Sta. Tech. Bui. T-12, 29 pp., illus. 



46 CIRCULAR 951, U. S. DEPARTMENT OF AGRICULTURE 








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48 



CIRCULAR 951, U. S. DEPARTMENT OF AGRICULTURE 



Table 18. — Dates of last killing frost l in spring and first killing frost in fall and 
length of frost-free period at Lawton, Okla., 1917-49 



Year 



Last frost 
in spring 



First frost 
in fall 



1917— 
1918— 
1919— 
1920— 
1921— 
1922. „ 
1923— 
1924... 
1925— 
1926— 
1927... 
1923— 
1929— 
1930— 
1931— 
1932. __ 
1933— 



Anr. 


8 


Oct. 


18 


Mar 


18 


Nov. 


18 


Apr. 


9 


Nov. 


9 


Apr. 


4 


Nov. 


1 


Apr. 


16 


Nov 


9 


Mar 


12 


Nov. 


13 


Apr. 


4 


Nov. 


5 


Mar. 


31 


Oct. 


23 


Mar. 


18 


Oct. 


27 


Apr. 


14 


Nov. 


4 


Apr. 


21 


Nov. 


11 


ADr. 


14 


Nov. 


2 


Mar. 


16 


Oct. 


23 


Mar. 


29 


Oct. 


28 


Anr. 


21 


Oct. 


30 


Mar. 


30 
14 


Oct. 
Nov. 


10 


Apr. 





Frost-free 
period 



Days 
193 
245 
214 
211 
207 
246 
215 
206 
223 
204 
204 
202 
221 
213 
192 
194 
207 



Year 



Last frost First frost Frost-free 
in spring in fall period 



1934.... 
1935— 



1937 

1933 

1939 

1940 

1941 

1942 

1943 

1944 

1945 :_._ 

1946 

1947 

1948 

1949 

Average 1917-49. 



Mar. 
Apr. 
Apr. 
Apr. 
Apr. 
Apr. 
Anr. 
Mar. 
Mar. 
Mar. 
Mar. 
Aor. 
Mar. 
Mar. 
Mar. 
Mar. 
Apr. 



Nov. 3 
Nov. 4 
Oct. 26 
Oct. 22 
Nov. 6 
Oct. 30 
Nov. 10 
Oct. 31 
Oct. 26 
Oct. 26 
Nov. 19 
Nov. 13 
Nov. 10 
Nov. 6 
Oct. 17 
Oct. 30 
Nov. 2 



Days 



218 
206 
203 
197 
212 
195 
212 
217 
209 
219 
234 
222 
247 
224 
203 
226 
214 



» A temperature of 32° F. or lower was considered to be a killing frost, unless recorded plant data indicated 
otherwise. 



Table 19. — Monthly average wind velocity at Lawton, Okla., 1916-4-9 



Year 



Velocitv 



Jan. 


Feb. 


M.p.h. 


M.p.h. 


7.8 


6.8 


5.8 


3.8 


7.8 


6.7 


4.4 


7.4 


4.9 


5.6 


6.4 


6.0 


6.4 


8.6 


5.4 


6.4 


6.2 


6.8 


5.7 


6.8 


6.6 


7.1 


6.3 


7 7 


5.9 


6.7 


8.2 


7.5 


6.6 


5.9 


5.8 


6.8 


6.3 


5.6 


4.1 


5.4 


5.7 


6.2 


6.5 


6.9 


6.2 


7.0 


7.8 


7.9 


6.9 


7.9 


6.1 


8.0 


6.2 


8.4 


5.3 


5.5 


5.4 


6.8 


5.7 


5.8 


5.0 


5.5 


4.8 


6.5 


5.4 


6.5 


4.4 


5.6 


5.1 


4.7 


5.8 


4.8 


6.0 


6.5 



Mar. 



Apr. 



May 



June July Aug. Sept. j Oct. 



Nov. 



Dec. 



1916— 
1917— 

1918 

1919 

1920 

1921— 
1922— 
1923— 
1924— 
1925— 
1926— 
1927— 
1928— 
1929—. 
1930— 
1931— 
1932— 
1933— 
1934— 
1935— 
1936— 
1937— 



1940- 
1941- 
1942- 
1943- 
1944- 
1945- 
1946- 
1947.. 
1948- 



Average . 



M.p.h. 
9.2 
10.0 



7.2 
8.0 
7.7 
8.1 
7.3 
8.6 
7.5 
10.2 
9.1 
7.9 
7.3 
8.1 
7.2 
8.8 
8.1 
7.0 
7.8 
7.1 
7.2 
8.2 
8.0 
5.7 
6.8 
7.1 
7.2 
7.2 



M.p.h 
8.6 
10.8 
7.9 
6.7 
9.0 
8.1 



6.2 
7.5 
6.8 
6.7 
9.0 
8.0 
7.4 
7.1 
8.4 
7.4 
6.2 
8.3 
7.9 
7.7 
8.1 
8.1 
6.8 
6.4 
6.9 
6.0 
8.8 
5.9 
5.2 
6.9 
5.9 
5.1 



M.p.h. 
7.2 
7.8 
9.6 
4.9 
5.5 
6.1 
5.5 
6.9 
5.2 
5.1 
5.3 
7. 1 
5.9 
7.4 
6.4 
7.2 
6.1 
6.0 
4.7 
6.6 
5.8 
5.8 
6.2 
6.5 
5.5 
4.5 
6.5 
6.8 
5.5 
6.9 
5.5 
4.5 
4.8 
4.6 



M.p.h. 
7.1 
7.0 
4.7 
3.3 
5.2 
4.5 
3.9 
5.2 
6.3 
5.9 
5.1 
4.8 
6.6 
6.1 
6.2 
6.4 
5.2 
5.5 
5.8 
4.9 
5.2 
4.8 
5.2 
7.0 
5.2 
3.3 
5.8 
5.3 
6.4 
6.4 
5.4 
5.4 
4.5 
3.6 



5.4 



M.p.h 
3.6 
6.2 
5.9 
4.0 
3.8 
4.3 
4.8 
3.3 
4.6 
5.5 
4.2 
3.7 
4.1 
4.1 
4.3 
5.0 
4.4 
4.6 
5.2 
3.2 
5.3 
5.4 
3.8 
5.6 
5.2 
3.0 
4.7 
3.8 
4.2 
3.5 
3.2 
3.6 
3.7 
3.7 



4.3 



M.p.h. 
5.3 
5.2 
6.1 
4.6 
4.1 
4.4 
4.1 
4.6 
5.3 
3.3 
3.9 
4.2 
3.6 
3.9 
3.4 
4.6 
5.3 
3.9 
5.5 
4.2 
4.4 
3.6 
4.9 



3.7 
4.5 
5.2 
4.7 
3.3 
4.2 
3.7 
3.3 
3.5 



4. 3 



M.p.h. 
5.8 
4.6 
5.3 
5.5 
4.7 
5.8 
3.6 
4.0 
4.4 
3.8 
4.4 
5.4 
4.0 
3.4 
4.7 
5.7 
4.0 
4.9 
6.2 
3.6 
5.4 
4.5 
3.7 
5.3 
4.3 
4.7 
5.0 
4.5 
4.8 
5.4 
3.9 
4.0 
3.4 



4.6 



M.p.h 

5.9 
7.7 
3.9 
5.9 
5.7 
6.1 
4.2 
4.4 
3.7 
5.0 
3.8 
4.5 
6.4 
4.0 
4.8 
4.9 
6.1 
4.6 
4.5 
5.9 
5.0 
4.5 
4.0 
5.6 
4.5 
4.2 
4.2 
4.9 
2.9 
3.6 
5.2 
4.1 
3.8 



M.p.h. 
6.7 
5.3 
5.6 
5.2 
5.4 
5.7 
5.0 
4.0 
5.1 
4.4 
5.8 
6.9 
6.9 
5.2 
5.1 
5.5 
6.1 
5.2 
5.9 
5.4 
5.2 
6.2 
6.5 
4.3 
5.9 
3.8 
6.0 
4.4 
5.0 
4.4 
4.7 
4.5 
6.3 
3.2 



4.8 



5.3 



M.p.h. 
6.0 
6.7 
5.1 
5.8 
5.9 
6.5 
5. 7 
6.6 
5.0 
5.8 
6.0 
6.4 
6.5 
4.7 
5.5 
5.2 
6.5 
5.2 
5.9 
4.7 
6.3 
6.2 
5.2 
4.9 
4.6 
4.8 
4.9 
5.0 
5.5 
4.6 
4.6 
4.7 
6.0 
4.6 



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